About once or twice a week my laptop will wake up in the early hours of the morning (about 6ish) from sleep mode. This happens whether the AC power is connected or not. It will then turn itself off after a few minutes. The only way I can stop this happening is to shutdown the computer every night, but I would like to leave it in sleep mode if I can I don't have to wait ages for it to boot up in the morning.
I can't remember what days of the week it does this or if it's random, I've been shutting down windows every night for a while now. I have automatic defragment turned off and my virus scanner is only set to run at midday.
I know it's a windows 7 issue because it doesn't happen when I'm running linux. How do I find what's causing my laptop to wake and stop it from happening?