windows updates, update your video card driver, run a defrag, get and run a good registry cleaner, etc.
These (along with some additional steps) just might help. It's very important to keep your operating system up to date. Video card drivers are otherwise the first thing to check, but honestly sometimes the most recent drivers are NOT the best (ATI anyone?). Try rolling back to a previous driver release for your card and see if that helps. If not, slap the latest back on. Unless you are using an SSD, make sure you defrag (I would recommend once a week, schedule it sometime in the early-early morning so it won't interfere with use). I've seen defrags work wonders on peoples' machines, depending on how severely it was needed. Another thing you might want to try is run an error check on your physical hard drive. If a drive's health is deteriorating it can lead to some very strange behavior.
Registry cleaners I would be a bit wary of. If you do run a registry cleaner such as CCleaner, make absolutely sure you create a registry backup so you can undo things if your comp decides to lose its mind.
Out of curiosity, what are your system specs? And are your hardware temps getting very high during play?