This issue occurred due to USB things plugged in. There's another reason for laptops and you can test for that issue by shutting down, removing the battery and testing again. If that fixes it, call the machines maker to begin a dialog. Sorry, I am not offering any fixes here save one. Place some USB hub inbetween the USB devices and said computer. And even that doesn't always work.
I have my Vista desktop to go to sleep after 10mins of inactivity. It was working fine about two days ago but now it doesnt go to sleep. is there a way i can find out what process is active that is keeping it from going to sleep?