If all else fails do, or have done by professionals, a wipe of your hard disc, after backing up all the files you don't want to loose.

I recently experienced problems with my computer, the cause of which was never found either by me or the staff at a very good computer repair shop. They finally did a wipe for me and my computer hasn't worked this fast and well since it was new. Hard drives tend to become bloated with useless junk and files get corrupted files over time, regular wipes are recommended. Mine had never been wiped in six years.