I braught a second Hand 20GB Seagate hard drive from a local shop. After having no problem with my comp before, out of the blue the hard drive started to make a crakling noise and it froze. I reset it and it said insert boot disk. After a bit of looking it somehow overwritten the boot sector.
After a few hours, i reformatted my hard drive and loaded all my stuff again. IT has been making the same noise and freezing again, but no overwiting anything. I am scandisking it everytime it does it, and fixing someerrors.

Is my hard drive stuffed, or is there a way to fix this?

It sounds like a head crash, which means it's dead, or it's having lots of bit problems. You should use this software from Seagate's website, download the DiscWizard Starter Edition. I'm not really sure if it has an option called, "Write Zeros". So if it doesn't it's in the other program, Seatools Diagnostic Suite. If it does, do a "Write Zero's", slowest option. If you have two hard drives, i recommend disconnecting the working one, then use this software. After starting the software, if it says something like no bootup, or something similar, then hard drive is dead.

Here's the url for Starter Edition,
http://www.seagate.com/support/disc/drivers/discwiz.html

Good luck,
Tim