It could be a number of things.  We recently got two of the new viruses in.  Unfortunately, a virus has to come out and wreak somewhat havoc before a fix is created to prevent it.  Although I thought I removed them completely, I was still having problems with the computer.  I finally gave up and let a tech deal with it.  It ended up that there were still remnants of the virus in our computer which was causing all kinds of problems.  In the end, he just backed up our files and did a whole system restore and checked everything out.  Everything is working fine now.

Maybe, this can help you out:

http://www.computerhope.com/issues/ch000380.htm

I was trying out IE8 recently for a few days.  I have completely lost all faith in Internet Explorer.  Internet Explorer 8 is a very feature rich browser with everything I needed, that was until it kept locking up.  My system is prestige in a sense and there is no reason for it to do so besides Internet Explorer being at fault.  I highly recommend installing and making the switch to firefox.  It just simply more stable.

After I downloaded IE 8 I had major problems and had to have my whole system overhauled and so I went back to IE 7. I'm still having problems with Runtime Errors but I've figured out the sweeps causing it.  It seems to only happen with the IW's so whenever I enter a new sweep (especailly a flash sweep) I enter only that one and check to see if it shuts down.  The new Carpet one sweep is now causing me the runtime error. I don't know anything about Firefox so I'm reluctant to switch over and try to learn a whole new OS.

OH!