OS turns off - Fans & case remain powered

My wife's homebuilt PC (18 months old) started having an odd problems last night. OS is windows 7 Home. Everything was fine until last night. No new programs installed, no new devices, just regular PC like everyday.
Here are the symptoms:

Prob 1)
- OS is turned off, PC shuts down.
- Case lights and fans remain powered. So does the CD drive.
- Power button does not restart the PC
- Power button pressed in 4 seconds will not stop the fans or lights. It seems to have no effect.
- Only solution is to turn the Power supply off directly at the back of the PC
- As soon as I turn the switch on, the fans and the lights come straight back. This is before even pushing the power button.
- If I press the power button, the PC boots up no problem.

Prob 2)
- If windows goes into sleep mode after not being used for a while OR if I put it into sleep mode on purpose, nothing makes the OS come back. I tried touching keys, using the mouse, pressing the power button, holding the power button....Nothing.
- Fans & lights remain on. CD drive remains active.
- Only solution is by using the switch on the power supply.
- When I put the power back on through the power switch, same effect as in problem 1) except that Windows resumes instead of simply rebooting.
- No ill effects.

PC seems to be running fine. Haven't tried any games.
I did take the whole PC apart and everything looked fine. The only thing changed was that it was less dusty :p

It seems too strange for it to be software related but I could be wrong. I have Norton 360 4.0 installed and updated.
My feeling is that this is the motherboard acting weird and dying but I am no expert.

Any advise I can receive would be great. The problem is highly annoying but the computer is still running fine.

CPU: Intel Core 2 Quad Q9550 Yorkfield 2.83GHz LGA 775 95W Quad-Core
Motherboard: GIGABYTE GA-EP45-UD3P LGA 775 Intel P45 ATX
HD: Western Digital Caviar Blue WD6400AAKS 640GB 7200 RPM SATA 3.0Gb/s 3.5"
Graphics: EVGA 896-P3-1257-AR GeForce GTX 260 Core 216 Superclocked Edition 896MB 448-bit GDDR3 PCI Express 2.0 x16 HDCP
Memory: Kingston HyperX 2GB 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Desktop Memory Model KHX8500D2/2G
PSU: CORSAIR Enthusiast Series CMPSU-650TX 650W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS
3 answers Last reply
More about turns fans case remain powered
  1. This is a long shot but uninstall the power management software that came with the motherboard.
  2. I just tried that and the problem remains the same. Still no change.
  3. Have you checked for a newer Bios for your board? I have seen update that fix issues like you are saying by flashing your bios to a more recent one. Hope this helps..
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