[SOLVED] System won't wake up

This being my first post on this forum let me fill in some blanks. I have had computers since day one. Still have my first one, an Atari. My newest is Win7Pro, 8g RAM, AMD Quad CPU. This system is great. I have had almost zero problems. What I have had was software related and minor. Now it's acting a little strange. After a period of inactivity it will not respond. I use a blank screen saver but no power down or sleep mode. The computer appears to have shut down. Optical mouse is dead, no fans. To restart I have to unplug in back and plug back in. Then the start button operates. Until the unplug I get no response at all. It runs about 45c as I have SETI running on it (searching for ET) at all times. I have massive amount of air for cooling (over 100cfm) I have found nothing odd in the setup and have confirmed power settings. I'm starting to think hardware failure. Any ideas what else to check? It always restarts and runs great.

Odd one!
Only thing I can think of is to keep the hardisks awake in the power settings.
Obviously (imo) the computer is still operative. Pulling the power plug is, of course, finally switching it off.
Have you tried a swift jab of the on/off button to wake it up? That does the trick on one of my laptops with similar bad behaviour.

Have not tried that. At least not a "swift" jab. We'll see next time. I'm starting to lean towards a PSU failure. I can't think of any other reason why an unplug helps. Resets the PSU maybe? I know it's not heat. With all the air I have flowing there is almost no heat venting from the PSU and the other fans venting have zero heat. If / when it happens again I have a spare PSU and will swap it out. I will check out the drive settings. Thanks for the ideas.
I must say that Win7 is by far the smoothest OS I have used.

The gremin has been found. Seems I was having power glitches. Not loss of power, just a burp. TV, clocks not affected. I saw the lights flicker and shortly afterward noticed I didn't hear my PC running. Had to do the unplug routine. About an hour later happened with me at the PC. Same thing. Shut down, no restart button, unplug, all is well. I think I need a UPS system!!!