I agree with roadripper and green1234 however if you can't figure out whats wrong with it and don't feel like spending money on geek squad you could always Factory Reset it which basically wipes the drive clean of anything you stored there and some how brings back everything you may have deleted that came with the computer, I suggest you only do this if you have everything backed up on another harddrive.
I recommend an internet search giving the problem that your computer is facing and the model of your computer. Be as specific as possible. This is a good thing to remember when it comes to buggy comps: I it happened to you, it likely happened to someone else.