Black screen BIOS

[Jason060514]

I'm recently bought a used HP Prodesk 400 G3 mini and am having a problem that might be as simple as a monitor change but I don't have another monitor and was wondering if somebody could give me the key presses to enter so I could do boot from USB blind or offer another solution. I currently use an Asus Rog Swift pg278q connected via display port and the screen won't turn on until after getting into the OS, I've tried entering bios bio boot screen every possible way including removing the cmos battery to no avail. 

[Hibb1]

Does it have an SSD HDD? Sometimes with certain monitors the PC boots too quick for the monitor to display any of the POST stuff.

Windows 10 defaults to quick boot, so even though you switch it off, it's kind of in a hibernation mode. Therefore it boots super quick. Removing the CMOS battery *should* have paused the boot with an error/message. Maybe leave it out for longer, or look for a 3 pin jumper block that shorts the CMOS.

Otherwise, with a USB WIRED keyboard, IMMEDIATELY after pressing the power button, furiously tapping ESC will bring up a menu. OR same as above but tapping F10 will bring you into the BIOS. 

OR Once it's in Windows 10, Hold down left shift while you click restart. This will then boot you to a Windows 10 trouble shooting menu. Click TROUBLESHOOT --> ADVANCED OPTIONS --> UEFI FIRMWARE SETTINGS. This will then reboot the unit straight into BIOS.

[Hibb1 · Accepted solution]

Oh, and re-reading your OP properly, the F9 is the button you want to tap to bring up the boot device menu. ESC will also do this, you just need to hit F9 once the ESC menu comes up.

[Jason060514]

Thanks for the reply and I'm sure it would normally work but it appears my monitor is someway somehow incompatible as I went to a friend's house and used their monitor with no problems. Again, thanks for the input as I'm sure it will be valuable to somebody in the future.