i had been searching for fix with windows 7 sleep problem.. it cant go to sleep everytime i hit the sleep button.. it was a nightmare for me.. but after searching so many sites and fix… i found one site that solve my problem.. from windows7forum..

Computer Won’t goto sleep ?
here is why and how to fix it

By default Windows 7 has media sharing turned on ( for xbox , ps3) ect

this pervents it from going into standby Mode

The Fix is Simple

Open control panel and goto

Power Options > change Plan settings > Advanced Power Settings

+Sleep
Allow hybrid Sleep > disabled
Allow wake timers > disable/enable try both settings

+USB
USB selective suspend > ENABLE

+When Shareing media [ This is the critical one ]

Set to allow the computer to sleep