Have you looked at the drive with the disk utility?
When you open the laptop
next time take a close look at the cable for pinched or broken wires, make sure the cable
is properly seated on the motherboard connector.
Try running the hardware test
app, comes on the restore DVD.
Boot to the dvd by depressing the "d" key during
bootup, keep the key depressed until you start to boot.
ifixit.com the have a series of troubleshooting guides for all mac models.
Studio G-fx 15inch quad-core i7 Macbook Pro Logic9.1.8, LPX 10.0.3