|Boot to some other media such as cd or usb flash and then copy all the data off you can.|
Then I'd start with some diag tests. Ultimate boot cd or other diag disk may be a good start. Start with memtest for a day or so. Then move on to the hard drive tests. Best to use the OEM tests for the hard drive. If you have a Maxtor then use their diags.
Why did it take me over a year to phone in a problem to ATT?