We’ve got a couple ASUS P5KPL-CM motherboards, and when we’d try to put them to sleep, well they’d wake right back up again. Immediately. Everything powers down, you get the click, then it immediately wakes from sleep. This happened both in Windows 7 as well as in Mac OS X Snow Leopard (a hackintosh install)
I wrote one before about sleep issues in Vista – It’s possible that a similar change in device manager would work in Windows 7, but here’s another way to fix it, in all your operating systems, for good:
It’s the little jumper you see here circled in green, located on your motherboard (I made sure to get the rear ports and CPU fan in the picture to help you locate it). By default, ASUS has in on the left 2 pins.
Pop it off and put it on the right 2 pins (as shown in the picture).
For whatever reason, ASUS is addicted to putting this jumper in the other position by default, which always causes problems with sleep. I don’t remember the specifics of what it does, but it’s got something to do with standby voltage being put through the USB ports.
In any case, both Windows 7 and Snow Leopard properly go to sleep after this change, and can still be awoken by hitting a key on your USB keyboard. If your P5KPL-CM doesn’t sleep, give it a try.