Computer Won't Power Down!!!

Hello.

I recently purchased a new motherboard for my current system, specifications as follows:

Intel Core 2 Quad Q9550
Gigabyte EP45-UD3R
4x1GB Samsung DDR2 800
Gigabyte 8800GTS 512
2 x WD HDD (1x 320GB, 1x 1TB)
ASUS DVD-R ODD
HuntKey Titan 650Watt PSU: 4x 12v Rails @ 18amps

After swapping out MB and fresh installing Windows 7, I noticed the computer won't power off. Windows shuts down and the monitor turns off, however the fans are still going – system sound like it is still on. I have checked power settings in control panel as well as trying different OS's, such as, Ubuntu 9.04 and Vista. The system still fails to power down. I've taken the system apart again and checked all cables, even trying different graphics card, but to no prevail. Bios has been upgraded to newest version (v11) and settings loaded as optimized default as well as downgrading to earlier bios, still nothing. I have heard people on other forums talking APM or APCI or something. How do I check if it's this? Does anyone half a successful EP45-UD3R running and what BIOS settings are you using?

Any help is greatly appreciated. Thank you.

-Naito