Reinstall the mouse driver.. battery operated? Change them. If its cordless check all the fittings and try it with the RF box in plain site of the mouse.
Just before you go to bed set the AV scan at
http://www.symantec.com to run a full scan. It could be something that is spoofing your HD scanners.
Also check the mouse plug to make sure the connections are clean (try another mouse if you have one as well)
We reinstall windows over itself every few months as well to keep that stuff from happening.
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