I format and reinstall my machine about every 6 months. I like to keep it very clean and tidy - maximise performance as well as stability. If I try software out I always go through after uninstalling it and make sure it is gone - most software doesn't uninstall cleanly. The rub is that a person has to know what they are doing when cleaning manually like that, one wrong move and everything won't work so well.
If you want to use a tool to check things out, download and install a trial version of Tune-Up Utilities. Of all these 'suite' type programmes this is one I actually use. I am not affiliated with them or make any money out of suggesting them, and I wouldn't suggest it if I thought it was rubbish or would damage your machine in any way (like a lot of these things can).
http://www.tune-up.com/products/tuneup-utilitiesSorry if this violates a no-advertising rule - but this is non-commercial. Moderators feel free to remove this link and reference to it.
Download and run some of the tools, you can find out where your file assoctaions have gone, clean junk from the registry and lots of other things. The good thing is that your computer will run better and perhaps won't crash as often.
Dave.