Welcome to TSF:
Please list what upgrades have been performed on your system since it was manufactured from Dell. The reason for this question being the Power supply unit supplied with manufacturered PC's if usually just about adaquate for the original spec for about 2 years. If you have upgraded video cards especially or more ram and more hard drives etc then you may have a hard drive which is under powered by the PSU.
A second thought being: download and run Memory Test (memtest86) free in my links below @ signature / diagnostics
Also you could download and run the Maxtor hard drive diagnostic utility to check the mechanical health of your drive >>>> run the extended test!
let memtest run for atleast two hours three is better
post back with your results and information