I suspect (but can't confirm, based on your information so far) that it is a hardware issue.
You state you had 2 monitors configured at the beginning. I presume this means you have access to two monitors, two video cables, etc. I state this because the problem hardware could also be the monitor (I have a dying LCD that I though was an OS problem for a long time...
As far as seeing the BIOS screen (or, actually, the boot up screen) at power on...this can be affected by having the addin Video card still installed, especially if it is designated as the default device in the BIOS (thereby bypassing the onboard chipset). If you can get into the BIOS, do so and check that. I still recommend removing the discreet video card, forcing the onboard to be the only device (and thereby forcing the bootup screen onto it).
After that, you may need to try various combinations of video cables and monitors, in order to rule out the possibility (or, confirm it) that the problem isn't a cable or monitor. After that, boot up with the onboard graphics only, and see if PCLOS runs OK for a bit.
After all that, you can consider putting the video card back in and see if the problem is there...
This is a troubleshooting process you will
have to go through to determine if the problem is hardware, and if so, what piece (or, possibly pieces) of hardware are problematic. If your hardware all
checks out OK, then the next step is to look at software (OS settings, drivers, etc).
Run through these steps, and report back in clear points as to:
1) What works
2) What doesn't
3) What combinations you test