Like someone stated above, it's possibly the motherboard. Now if they change MB and it still happens, then just get another system. Run a diagnostics on the MB and see what happens. Also, try updating the hard drive's firmware.
Click the Start button and all programs and go to Accessories and find Command Prompt. Right click on it and run as Administrator.
Type chkdsk /r. This process can take 1 to 2 hours.
To see what other options you have, just type chkdsk /?.
See if this helps.
If errors are reported, it's possible they sent you a refurbished hard drive. Get another replacement.