|Sounds to me like it's your hard drive. If I were you I would back up all of my important data, and contact the computer manufacturer to see if you can get a new hard drive out of warranty.|
From my experience and from what I've read, what you're experiencing is a sign that the hard drive is failing. Unfortunately, it will most likely continue getting worse until it's unusable.
You can try running a tool that will check your hard drive for you, such as SeaTools:
Or you can check to see what brand of hard drive you have and check their website to see if there is a tool more specific to your drive.
Hope this helps.