One great thing about a laptop is putting it to sleep. Close the lid, pack it in your bag, and you're saved the trouble of rebooting it later. But if it doesn't go to sleep properly, it can heat up in your bag, burn your hand, or even damage its hard drive. Here's how to troubleshoot MacBook sleep problems.
The first step is to make sure you don't have an application running that's accessing the hard drive. If you're downloading a file over Wi-Fi, that can interrupt sleep. Playing music from iTunes or playing a DVD also can cause sleep-interruption. Close programs to eliminate them as a possible culprit.
Bluetooth devices shouldn't wake a sleeping computer, but some Bluetooth mice do. So make sure you don't have any on. Then go to system preferences, click Bluetooth, click settings, and deselect "Allow Bluetooth devices to wake this computer."
Another issue could be the spotlight function. It's a handy way to search the hard drive, but if it's indexing your hard drive, the Mac won't go to sleep.
If you're sharing an Internet connection, a file, or even an iTunes library, that can stop sleep from working. Disconnect any users or turn off sharing to see if this is the problem.
Another issue is external devices. If you have any USB or FireWire peripherals connected, such as an external hard drive, it may cause problems. Disconnect them, properly, one at a time to make sure they're not the problem.
And finally, PCI cards. This was my problem. Expansion cards, like my EVDO card, may have drivers that prevent the computer from removing power from them, thus stopping sleep. You'll need to look for updated drivers, or just remove the cards in question.
If none of this works, you may need to reset the system's power management. Look for ourfor more on that.