z820 boots up to Win10 but shows no BIOS POST messages

[Paddywack01]

Hi all,

I have recently had a problem booting up my Win10 z820 (see specs below). It will boot into Windows 10 but sits on a black screen for quite a long time with no POST messages from the BIOS. Occasionally it will not boot up at all. I have to restart quite a few times until I can see the HDD light flashing. I've reset the CMOS and taken the battery out and replaced. I've run HP Performance advisor  and all the components seem to be working OK including the SDD C drive. I've checked the BIOS settings in Performance Advisor and POST messages is enabled.

Anyone got any ideas what might be going on? Thanks Nick

Model: HP Z820 Workstation
Baseboard ID: 158B
BIOS version: J63 v03.91 (Current Setting Group: Media Composer)
Processor: Intel(R) Xeon(R) CPU E5-2643 v2 @ 3.50GHz (2 processors)
Enabled Processor Count: 24
Total Memory: 128 GB
Local Storage: 5.92 TB (3 drives)
Graphics Card & Driver: Quadro M4000 -- 462.31
Slots in use:
SLOT 3 (PCI Express Gen 3 x16): NVIDIA Quadro M4000
SLOT 5 (PCI Express Gen 2 x8): Blackmagic Intensity Pro 4K
Operating System: Windows 10 (64-bit) - Microsoft Windows 10 Pro

[Paddywack01]

Just to add. Because of this problem I can't access the BIOS at boot up. None of the boot up commands seem to work. This is with a USB Keyboard which works fine otherwise. I've also tried a different graphics card but this makes no difference. to the black screen boot up.