Windows Vista Problem: standby = logout

I've just upgraded from XP to Vista on my home theater PC and I'm having problems with standby mode. When I try to put the computer in standby the screen (tv) goes black and everthing spins down as it should. But a second later, the computer starts up again and I'm presented with the login screen. Does anyone have any ideas about what could be causing this?

 

It has to be something else since no applications are running when I put the computer to sleep. And it's not that I'm logged out (my mistake), the computer just wakes up directly after I try to put it to sleep. The login screen was just there because I had checked "require password on wakeup" (or something similiar).

 

Agree with Steve R Jones. Suggest you download winpatrol.exe (just type it in google to find it) and rt-clk the icon on the taskbar after it's installed and choose display startup info and disable or stop one by one the processes running in the background, especially the non-windows ones, till the computer stays asleep.

Keep winpatrol. It's good antispyware too.