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>This happened with this computer before.
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>May be I need to re-start PC more often, I usually just lock computer when I go home...

If it is an XP machine it wouldn't hurt to restart daily although XP is a pretty rock solid OS.

If it is a STABLE Vista installation (I haven't worked with one that wasn't but I know some people have serious issues) then I wouldn't worry about a restart unless you are having really serious issues and can't find any other culprit.

BTW I only use IE7 and do not have any other browser installed - that is why I'm wondering about FireFox and IE not playing well together..