Possible Duplicate:
Troubleshooting a Windows 7 PC that wouldn’t sleep
Recently, my computer started to refuse to stay in sleep mode. Every time it goes into sleep, it is wakened right away. I just reinstalled Windows 8 without activating media sharing and the behavior remains.
What I discovered is that if I clear the CMOS, the first sleep period will last but any subsequent one, even if I restart the computer, will behave as explained. So, every time I clear the CMOS, I get one sleep period and that's it.
Anybody have an idea for what to try next?