If (as I found by investigating another issue) I find I can't access bios, and I get the 'PXE-E61: Media test failure, check cable / PXE-M0F: Exiting NVIDIA Boot Agent' error, then is this (from the net) a sensible option:
'Power down
Unplug power cord
Open computer case and remove the CMOS RTC battery (about the size of quarter)
Press and hold the power button for 10-15 seconds. This allows all capacitors to drain
Put the battery back, plug the power cord in and power up
You should get a CMOS checksum error and a press f1 to continue f2 to enter setup message.
Press F2.
Load defaults, set date/time, check all other settings, save and exit.'
and is this high among the likely causes of error in any of your experience? As various possibles come up when searching, though some/most are related to not being able to boot up at all, which I can, no problem.
Thanks.