My husband usually leaves his computer on all the time and when he woke up this morning, it was off, so when we hit the power button, it looks like it is going to start up normally - the disk drive buttons flash, the keyboard buttons flash, the monitor clicks like it is going to turn on - then the computer just shuts off before anything comes up on the monitor. I opened the case because it was FILTHY! I cleaned all the fans because they were covered with crud and tried again, but it's the same thing. :cry I can tell you he runs Windows XP Pro, but it's an older computer that was built by a friend of his. If you need more info on it and can tell me where to look, I will. Thanks so much!!