Computer was idle for a few hours, when I returned I noticed an unusually loud fan noise, turned on the monitor but it received no signal. Assuming that the computer had crashed, I restarted by holding down the power button, but on startup the monitor still displayed no picture, even in BIOS, and the fan noise remained. After connecting the monitor to onboard (motherboard) VGA port, everything except the GPU worked.
In kern.log and syslog were the following messages, from about an hour before I returned to the computer:
kern.log:Aug 17 12:39:04 jg-desktop kernel: [433566.176567] NVRM: GPU at 0000:01:00.0 has fallen off the bus. kern.log:Aug 17 12:39:04 jg-desktop kernel: [433566.176578] NVRM: GPU at 0000:01:00.0 has fallen off the bus.
kern.log:Aug 17 12:39:30 jg-desktop kernel: [433592.076011] BUG: soft lockup - CPU#1 stuck for 23s! [Xorg:1181] kern.log:Aug 17 12:39:58 jg-desktop kernel: [433620.076011] BUG: soft lockup - CPU#1 stuck for 23s! [Xorg:1181] kern.log:Aug 17 12:40:30 jg-desktop kernel: [433652.076010] BUG: soft lockup - CPU#1 stuck for 22s! [Xorg:1181]
(each followed by debug messages)
Those messages have not reoccurred since, however the following sometimes repeats every few minutes:
kern.log:Aug 17 12:42:00 jg-desktop kernel: [ 36.422543] NVRM: No NVIDIA graphics adapter found!
EDIT: Tried uploading nvidia logs here, but it still says “Scanning… Please wait”, so: http://www.sendspace.com/file/frfbbr