It could be a power supply or bad memory or too much dust or a bad connection (wiring expands as it gets hot).
You need to provide as much info as possible such as how long it runs before shutting off, if it does it only while doing certain functions or using specific programs, etc.
Have you actually done any viral scans with updated virus software? ) try an online one at http://housecall.trendmicro.com )
If a tech charged you for work for a cure but didn't cure the problem have you taken it back and complained that he/she didn't fix anything?
I need help. Our computer will suddenly shut off with no warning and no message to indicate what the problem is. We've taken it to get looked at and they can't determine what's wrong. I don't have Windows XP, which apparently rules out one of the viruses having that characteristic. The tech repaired the fan, alluding that the computer was shutting down because it was overheating. But, it still shuts down even after he did that. Is this a virus or what? My computer is only four years old. Anyone's advice would be great.

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