AMD 7750 (Not overclocked)
ASUS M3N78-EM motherboard (NVidia chipset + NVidia graphics 8300)
Corsair XMS Memory 4GB DDR2 (2 X 2 GB)
Sapphire Radeon HD6670 Graphics card (66W TDP - takes power from the PCI-E slot - no extra connectors)
1 SATA II Seagate HDD 500 GB
1 IDE WD 80 GB
1 SONY DVD-RW drive
4-5 USB devices plugged-in
3 120 mm case fans (2 Antec + 1 CM)
Cooler Master PSU model - CM 350 PLUS
APC UPS BackUPS-ES 500 300W
Windows 7 and 8 Developer Preview
All components have a varying age. UPS is a 7-year old (w/ new battery). PSU 1.5 year.
Everything was working fine until some time ago when the system had "no display" but I could hear the Windows startup sound. The system was booting but there was no display. Took out the graphics card and system booted normally (with display). Worked for a couple hours. Then to test again, I plugged in the graphics card and this time again the system booted WITH DISPLAY! Restarted the system. Again, NO DISPLAY! To sum it up, with the graphics card in, if I allow the system to remain switched off for a few hours, the system boots properly and functions in the way it should. But, if I had to restart, say to complete a Windows update, the system would boot but without the display. Let it cool off and boot after few hours, it works fine again.
What's the problem? I guess it's the power supply not able to put enough power for the graphics card. But then again, why it boots after long "cool-off" time? I've checked by unplugging some of the peripherals but the symptoms are same as above.
For once, I kept my UPS switched on after shutting down my PC. Eight hours later, the PC booted but without display. It seems that the "bad component" requires that it must be cut off power for its "cool-off" time.
What should be the cause - the graphics card or the SMPS or the motherboard itself?