System occasionally struggling to wake from sleep

Intel Core 2 Duo E6750 (overclocked stably to 3.2GHz)
Asus P5K Premium WiFi motherboard
nVidia 8800GT graphics card
BeQuiet Darkpower 650 power supply
4Gb Corsair RAM
1 x Samsung Spinpoint 500Gb
1 x Seagate Barracuda 1Tb
Antec 902 case
Windows 7 Home Premium


I have literally no idea which is the appropriate forum to post this in.

This is a system that I built myself, and which has been running with no problems except for one increasingly infuriating intermittent one. Very infrequently, perhaps once or twice a fortnight, it refuses to wake from its sleep state without a titanic struggle. The screen remains either black or frozen on the desktop while the fans speed up alarmingly until they are literally screaming (the temperature of the exhausted air remains unremarkable though). This lasts until either the system suddenly pops into life and the fans settle down, or I lose my nerve and force a reboot. After that, everything works again as normal.

My fault diagnosis skills only take me so far with this one. I know it's not the motherboard, as I had the same scenario with a spare Gigabyte m/b I had to use for a couple of months while my regular one was being repaired. Also, I don't believe it has anything to do with the overclock, as I can compress and convert video all day without a glitch. It's just when the system goes idle that the problem appears. It's not the Seagate drive, as that was installed fairly recently.

It seems that the culprit is one, or a combination of, the power supply, the graphics card, the Samsung drive, or even Windows 7.

My sanity is now hanging by a thread, so any insight will be greatly appreciated.

Steve S.