It only started happening a couple of weeks ago, it seems, but now whenever I put my iMac to sleep, it wakes up about 5-10 seconds later but the second time I put it to sleep, it'll stay asleep. Same deal even if I have no apps running. Any ideas?
Nope, usually I just press the power button on the back but the same thing happens if I go through the Apple menu as well.How are you putting it to sleep?
If you're using the keyboard shortcut, and you hold one of the keys too long, it will cause the computer to wake up.