What are the results of the last disk check. If there is seriously something wrong, please confirm, with your hard disk then please replace it with another hard disk.
You may consider cloning the entire contents of your current hard disk and then using a cloning program to transfer the data over to the new hard drive.
Try this cloning program:
http://www.symantec.com/home_homeoffice/products/overview.jsp?pcid=br&pvid=ghost10Clone onto several CD-Rs preferably, the first disc should be a bootable one.