It use to randomly restart on occasion but
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this could indicate dust buildup or hardware finally gone totally bad ,so start with opening up and cleaning dust buildup, tools to use are a paint brush and a vacum,give it a try and see what happens

Thanks, that was the first thing I tried. I thought maybe it was overheating but to no avail. Without being able to boot-up I can't diagnose the problem. I guess it is time for a new machine.

if you have the windows disk you could try booting to and going into the recovery console and doing a "chkdsk /r" at the prompt

are you using a usb keyboard or a ps/2 one ,if usb ,maybe you could try a ps/2 keyboard and see if it works