smz

In addition to testing the drive with Western Digital's Lifeguard tools. You could also schedule a offline windows scandisk that will occur upon your next reboot if you don't want to do this from a software side of things. If you can get to the run command or under accessories, choose command prompt and type the following chkdsk c: /f - if you have more than one drive do it one at a time, i.e. chkdsk d: /f. The bootable partition will not be able to be tested while windows is up. so it will ask if you want to schedule the check during the next reboot. OF course your would say yes.

Second scenario and I'm sure there are some free programs to do it. I personally use R&Wipe and Clean and/or Webroot Window Washer. Those puppies go through your entire hard drive looking for useless left behind files as well as giving you the option to delete past history for most of your installed programs. Some see this as a privacy suite though you would be surprised how many gigs people get back from temporary files alone.

Final suggestion is a defrag. You should to the chkdsk or WD diag first though. But the stock windows defrag is under accessories/system tools named Disc Defragmenter.

Hope the post above me helps and my post above this sentence also helps. Good Luck!