Try running the Dell diagnostic test, and download the diagnostic program from your hard drive's manufacturers web site. If it is Western Digital you can download WinDig here
. You can also hold down the windows key ( the one with the flag on it) and press R key. In the box that comes up type msconfig then go to the startup tab and take as much as you can out. Mine has my anti virus and windows sidebar open at startup and nothing else. That does not mean they won't work, but only that they don't start at startup.
Edit: You should also take off all the programs and services Dell puts on your computer that you don't need or use.