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HP Z420 Workstation
Microsoft Windows 10 (64-bit)

Today I switched my display from HP LA2405 to Z27 (4K). But the workstaiton refused to boot up. It will wait and beeping. I have to unplug the Z27, using the old LA2405 to boot and plug in Z27 again. The display works but it is jut cannot boot up. I am using NVS 510 video card. Thanks!

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during boot, the computer tells the video card to query (talk) to the display device to determine it's abilities and see if it can work with the card. i suspect the current video card is unable to resolve the received video information data from the new monitor. 


are you using the displayport  video cable that came with the new monitor? if not do so, this will allow a direct connection from the 510 cards displayport to the monitors displayport without using a displayport to DVI adapter


you might  try a alternate video connection if your card has DVI and displayport connections,... as sometimes using displayport instead of DVI (or vice versa) will work because each interface has it's own video revision standard

the DVI standard for this card whenn using the displayport to DVI adapter  is 1920x1200


a newer/diffrent video card should also  resolve your problem, look for a model that states 4k compatability and uses displayport as it's video connection

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YDuring boot, the BIOS controls the resolution sent to the monitor and as such it’s normally an old school 800x600. If you have boot failure and don’t see any BIOS boot sequence on the screen, maybe there is some BIOS setting that can help. It could be that your new 4K monitor can’t handle old school 800x600 (though that would be odd indeed)... but as a first step check BIOS for some video setting as they may help. 


What UEFI does I don’t know but some UEFI mobos have a higher resolution GUI based firmware... but check settings in the same way and confirm base firmware resolution is supported by your monitor.... and check your graphics card firmware supports UEFI (a cause of black screen boot failure when booting in secure mode), 


Only once OS has taken over from dumb BIOS does the OS request the video card to check the monitor EDID info (for the port in use) which lists supported resolutions. And at that time, the highest possible resolution should be user selectable within the OS driver. Note that the OS will select the previously set resolution if suppoted by the hardware (card and monitor) otherwise it defaults to something else (maybe the default safe 800x600). 


So your old video card should work with your new monitor unless you have UEFI and it is doing something odd. As such there should be no need for a new graphics card unless you want to output native 4K resolution so as not to have the monitor scale the picture. Whether your graphics card actually supports 4K output I don’t know but you should always see a boot sequence. 


(Edited silly iPad auto correct)

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skylarking, please read the link below it will explane how modern monitors are able to send their capabilities to the computer using EDID, during the bios boot phase, and after the windows OS loads

(at that point the video driver becomes active, and it to can also query the EDID information)

the reasion the bios reads the EDID is because not every computer runs windows and  the card has to know what display device/capabilities is connected when first powered up




again, information on what UEFI does, in a nutshell it's a modern replacement for the original BIOS interface

note that the original BIOS is still there, but on a UEFI based system all the original bios code does is call the UEFI extensions



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@DGroves, your first link does not make any references as to how and if BIOS fetches EDID from the monitor, if at all. It simply defines the EDID data structure and history but if i’ve missed something or you have something more specific, I could look at it (just be more specific than pointing to a rather long wiki)...


IIUC, the BIOS loads text to screen via TTY commands in real mode but uses VGA BIOS to draw on the screen in protected mode. VESA bios extensions can be loaded for more capabilities but everything supports VGA and was the go to method for BIOS boot sequence on everything i’ve owned. Protected mode is entered rather early in the boot process where the VGA ROM is used to set the resolution. As such early BIOS’ didn’t check monitor capabilities as they simply set a known safe VGA mode, usually 640x480 or 720x480. Once the OS took over (login screen) the installes OS graphics driver took over and we had all these wonderful resolutions available. Later video ROMs may have had some smarts but as i’ve mentioned all systems I have used have defaulted to a dumb safe 4:3 VGA mode to display the BIOS boot sequence. 


AS for UEFI, i do know a little about it and CSM and secure mode but how UEFI handled the video ROM and whether it fetches EDID i don’t unknow. I suspect UEFI does more than CSM classic styled BIOS VGA mode, especially for the few mobos that handle HDMI and it’s CEC capabilities.


@chenjin should clarify how his system firmware (BIOS as it is often incorrect but comonly called) is set up... CSM or secure mode... 


But i doubt the chenjin needs to know such minutia  on how boot process works... since, even if EDID is fetched during boot, one should still see something of the boot sequence on the screen and boot should proceed to OS login screen as expected.


So either there is a firmware fault, in which case I’d update the mobo firmware and graphics card firmware as a first step, or their is a firmware configuration fault in which case check firmware settings. Alternatively the monitor has some other quirky fault in which case it would be best for the OP to discuss it with the seller as monitor firmware is not user upgradable... 


At the moment, there should be be no need for the OP to buy a new graphics card as it should still work... 


[edited to add following]

Interesting that LA240 supports 640x480 and 800x600 while z27 does not support 640x480 ?

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That's an unusual problem.


Checking the specifications for the NVS510:




"Resolutions Supported: 1024 x 768; 1280 x 1024; 1280 x 720; 1280 x 768; 1280 x 800; 1440 x 900; 1600 x 1200; 1600 x 900; 1680 x 1050; 1920 x 1080; 1920 x 1200; 2560 x1440; 2560 x 1600; 3840 x 2160; 640 x 480; 720 x 400; 720 x 480; 800 x 600"


Both the NVS510 and Z27 appear to be working. And, because the Z27 will work when connected after booting, as the other posts have established, the problem is in establishing the link.   


And, that is the surprisingly feature of this problem. Windows will apparently establish a display link in as many circumstances as possible.- even when there is no  OS.  It's possible to boot to BIOS without a hard drive In every instance I've ever installed Windows, every monitor will initially run at 800 X 600. Six months ago I  set up a z420 (GTX 660 Ti) with a 4K monitor (Samsung 4K, 40" television) and it ran at 800X600 during setup. Connection then was by a Displayport to HDMI cable. Today the connection is HDMI to HDMI.




1. Try booting to BIOS with the OS drive disconnected.


2.  Just to eliminate a driver conflict as a possibility, consider reinstalling the NVS510 driver, ensuring to select: "Clean Install", especially if that system has been used with other GPU's. That will clean out the remains of old drivers that might conflict.


3.  If you have alternative cables, perhaps try different connections. Especially try the HDMI 2.0. The Z27 connections:

(1) HDMI 2.0
(1) Mini DisplayPort 1.2
(1) DisplayPort 1.2
HDCP 1.4 for DisplayPort and HDCP 2.2 for HDMI.


> Scroll down the chart and note the more extensive number of supported features of 4K by HDMI 2.0. this is the reason I use HDMI with my  z420 to 4K monitor.


4.  With the Z27 running, try restarting in Safe Mode and if it restarts with the Z27, then it may be possible to look into control Panel / Display, and Device Manager / Properties /Proprties. Ensure that the Z27 is identified as the monitor, only the NVS 510 is listed as the Display Adapter, the driver is the proper NVIDIA one (R390 U7 (391.89)  WHQL) and not generic.






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all UEFI and pre UEFI bios's that support EDID read that information from the display device. I have a asus x99 board that when in the bios displays the bios graphics pages at 2560x1440 without me having to set any settings and if i connect my 720p monitor the bios, the display will now be at that monitors  1920x1200 resolution.  this magic is done because the bios reads the monitors EDID information when the bios starts up. the wiki page i linked to does cover this but it is a rather in depth page and can be hard to read/understand


here's one that is a bit easer to read, the sections, 

What EDID Information is Exchanged Between Display and Source,... and    EDID/DDC Protocols


cover what data is exchanged on bios start up and from the windows video driver





i agree his video "should" work, but should does not mean will,........replacing the video card is a last resort and is why it's mentioned last. i suspect the issue is something else like using the 520 cards display to DVI adapters,.... if he is using one that will  limit the resolution to less than the new monitors 4k resolution

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Thank you all! I learnt a lot now. I am uing UEFI and will check what the EDID setting is when I got a chance to reboot. 

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I think I fixed that issue. Thanks everyone's help again!


In computer setup (F10/BIOS) there is no EIED settings. I think what the fininal work is that I changed the VIDEO ROM DOWNLOAD option from EFI to Legacy (I believe it is BIOS) this way fixed everything. I think it is werid, but I am not totally strange for I have 32GB memory so sometimes the BIOS do not have memory to use when they first trying to "download". That maybe the issue of PC archtecture or Z420 is still too old.... 

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strange, the nvs510 card is UEFI capable as it's a modern card.  however legacy mode does initilise the display subsystem a bit diffrent than UEFI does and it may verry well be that UEFI  mode may have a setting that was the cause in your  video issueat boot


Last, the HP z420 is really not that old, it's just now being phased out of active support by HP and the z420 was released in 2013 so it's now about 4.5 years old but still holds it's own overall.  Only the lack of nvme boot support  might cause a user to replace the system

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