The problem I'm having I haven't been finding anywhere else online. My computer always resumes from sleep fine and I never get errors or blackscreens. However, my computer wakes up in the middle of the night or early morning by itself, and then I find it hours later still on. I checked the Event Viewer to find that the wake source was "ACPI Lid", but no one touched the computer, and the only other events or tasks that run around that time seem to be regular startup tasks (so I don't know WHAT woke up the computer). This happens every night and the wake source is always logged as the lid.
This wouldn't be a problem if my computer knew it should go back to sleep afterwards, but it doesn't. Even if I set my computer to sleep after 1 minute of idleness it will just sit there indefinitely. To make matters more confusing (for me at least), if my computer is running on battery power, it will sleep after the time designated in the power options, so my solution is just to leave it unplugged overnight so when it wakes up it will go back to sleep. However, I would still like a real fix to this problem and haven't been able to find one anywhere.
My system is a Dell Inspiron 1505 (with the newest bios updates etc) and my graphics card is an ATI mobility 1400 (not that I think that has anything to do with it but then again it seems like a lot of people have been having graphics card issues). I'm running Vista Home Premium, and I've set a bunch of the media center update/download times to random afternoon hours to see if that was it but alas, my computer still wakes up in the middle of the night.

Can anyone offer any help?