Disk read error for Windows XP?

I recently tried to restore my Dell dimension C521 desktop to factory settings. After trying that, the screen said that the restore was not successful. After this happened, when I try to boot my computer, I get a message that says "A disk read error occurred, press Ctr+alt+delete to restart." I don't have a backup CD for my computer. I did a diagnostic check. My hard drive seems to be fine. I called Dell to get help, but they won't assist me, due to my warranty being expired. How can I fix this error? Is there a number I can call to get free tech support?