It could be in the BIOS (wake up at ...). It could be the Windows update setting (update at 3.00 AM).
But if you can use hibernate in stead of sleep, it has 3 advantages:
1. Cheaper (less electricity used)
2. Faster startup
3. No wakeup in the middle of the night.
Kees
hp pavilion desktop, I put compter to sleep about 8pm , every morning between 2am and 4am some thing is turning it on. How can i stop this? Its not keybord or mouse. batterys out . Norton perfomence shows svchost.exe, msnmsgr.exe

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic