I've had a problem with my laptop (running Vista) lately. I put the thing to sleep, close the lid, unplug all the cables, put my laptop in my bag only to get home and find out that my computer is still on. Or, even worse, it's off and the battery is totally dead.

I finally tracked this down to the network cable. Turns out there is a "feature" that your computer will wake up any time the network cable is plugged in, or unplugged. For people who plug-in at work, this is a really lame feature. Now if I have the audacity to unplug my cable *after* I shutdown my computer (who would ever do such a thing), my computer's on and the battery is wasting away.

Luckily you can change this behavior.

Go to the search field in the Start menu and type in Device Manager.

When the Device Manager opens, scroll down to the Network adapters section and open it.

Find your network card in there and right-click on it and then select Properties from the menu that is shown.

In the Properties panel, click on the Power Management tab.

Uncheck the box next to Allow this device to wake the computer.

That's all there is to it. Once this change is saved, putting a cable in or taking one out will no longer cause your computer to wake up. So if you're having a problem with your sleeping computer mysteriously waking up, try making this change to see if this is what's causing it.