What it does when I turn it on now, is the power light comes on, it makes a couple of little grunting noises (sounds like hdd), and then it just completely powers itself off. Screen displays no post/bios info.
My wife was the last person that used it, and she says that when she was using it IE froze (as it has been doing quite a bit lately) and she shut the laptop down by holding down the power button.
I've tried disconnecting all the extras (not many, just usb mouse and camera cable), and also tried removing the battery and running it only on mains. Obviously had no luck though. The only things that have changed on the system lately are that I upgraded my antivirus software about 2 - 3 days ago and at about the same time I defragged all the partitions on the beast.
The machine has been wonderfully reliable for as long as I have had it to this point. I have only rebuilt it once since I have had it, and that was about a year ago.
I realise that troubleshooting is difficult with such limited information as this but it is all I have to go on at the moment. Any suggestions would be greatly appreciated.