if you can get it started again try this
click start > open my computer> right click on your hard drive icon (probably c
> select properties> select tools> under error checking select check now> select both options available and select start
at this point you will likely get a message that informs you the disk check will start the next time you restart your computer, exit out of that message and then restart your computer, upon restart your computer will go through 5 diagnostic checks some fairly quick a couple are rather long
you could also try using system restore