Trouble starting computer after shutting down Windows 7 64 bit

[pojut]

I recently upgraded to Windows 7 64 bit. I shut down my computer as normal, but then when I later go to press the power button to turn it back on, nothing happens! It's like the computer isn't even plugged in. However, if I disconnect the 24-pin ATX power connector going to my motherboard and plug it back in, voilà! It turns on with no problem. I didn't have this issue with Windows XP SP3, and I didn't change any hardware when I installed Windows 7.

Anyone have any ideas? System specs in sig.

 

[pojut]

Bump in the hopes that someone can help :'-(