Check power options in control panel and look at you sleep mode options and make sure sleep mode is set correctly other wise there may be OS issues. i had the same issue and i reinstalled vista and it fixed issue
If I put my computer to sleep either through the start menu or if I do it by closing the lid the computer stays asleep until I plug the AC adapter in. Once I plug the AC adaptor in the computer wakes up. This is getting quite annoying because sometimes I just want to plug the laptop in without waking it up so that it can charge. But now I have to make sure the AC adapter is plugged in before putting it asleep in order for it to stay asleep. Can anyone guide me as to how to fix this? From my recollection the laptop did not do this before. I tried rescue and recovery back to an early point and its doing the same thing. Next step is a full factory restore. I hope someone can tell me how I can fix this so I do not have to do a full restore.
The laptop is a thinkpad SL400 with windows vista.