Hiya,
Have you installed any new hardware into your computer? like memory or hard drive upgrade? If so that may be the cause, if not then it sounds like a memory problem - unless you know the in's and out's of a computer I would suggest getting your local computer repair guy to have a look
Norton has also found to be a cause in some cases:
http://www.experts-exchange.com/Oper..._21485954.html
(scroll right to the bottom of the page)
Would also suggest you upgrade to Service Pack 3
(
http://update.microsoft.com)
I would also suggest this post to be moved to IT