|Sounds very much like hard drive failure, Alex.|
You can't test it while it's installed in the tablet since it has no CD-drive (since Windows won't start, you can only test the drive with a bootable CD).
To be absolutely sure it's failed before buying a new one, ask a friend if they can test it for you by putting your drive into an external USB enclosure. It can then be tested with SeaTools for Windows from here (click "Downloads"):
Or take a chance and just replace the drive without testing it. Testing it, however, would remove any risk of wasting your money.