My pc randomly restarts itself , no warning and can be anytime.

When it does it removes my log in details from forums,etc.

Anyone help its doing my head in. I have the free AVG software and adaware. Scanned with these but made no difference.

Please any ideas

 

chris/dawn ,my laptop randomly shuts down aswell,but i dont lose any details .it turns out that the fans are clogged with dust and the operating shuts it down to prevent it overheating.just an idea to check your fans.
cheers james