Very likely your drive has bad sectors, you should check hdd surface and smart status with some tool as MHDD:
http://hddguru.com/software/2005.10.02-MHDD/Boot mhdd from CD (or usb key if you know how to make it bootable) and press F8 to check SMART, expecially check for "reallocated sectors" and "pending sectors" and take nother picture of the screen, then press F4 twice to check surface for sectors errors and do a picture of the screen at the end.
Then post the pics here, someone may tell you what's wrong with the drive.
If there are many bad sectors the best thing to do is to not use the drive anymore for saving important data!!