The hard drive may be starting to fail or has already failed, so you need to test it to be sure, using the drive manufacturer's
Diagnostic Software for DOS. The links are here:
http://www.tacktech.com/display.cfm?ttid=287
Create a bootable CD from the diagnostic software's ISO file using
IMGBurn on a working PC:
http://www.filehippo.com/download_imgburn/
Boot your faulty computer or laptop from that CD and the diagnostic program will eventually open.
Test the drive with the Long/Extended test.