Perhaps you've noticed that files aren't opening as fast as they once did and things in general seem to be running slower.  The culprit is often errors and fragmented files.  The solution is easy: running a thorough Scan Disc.  And don't think just because you've seen your computer run a Scan Disc that this was the thorough version.  It is the quick version that only scans your startup files.  In our quest for maintaining our computer at it's peak efficiency, a quickie scan will not do. 

Depending upon how many files and the size of the hard disc, the thorough scan can take anywhere from one to several hours. 

Since you will not be able to use the computer during this function, I recommend that you run it overnight so it doesn't interfere with your work.  It's worth the effort.  A thorough Scan Disc will check for all errors on your system disc and will check for cross-linked files and attempt to repair them.

To run Scan Disc, run in safe mode for best results, restart your computer, and press F8 as it begins to startup (while the screen is black) until you see options for startup appear.  Choose Safe Mode.