If your getting the same error with a new drive you bought off ebay then it probably is not the hard drive. You are going to have to one by one rule out a few components like ram, cpu, power supply, and motherboard.
I would first try applying new thermal grease on the cpu and try reseating the ram. Then look to see if you have any blown or bulging capacitors on the motherboard. Then maybe try another power supply.
To answer your question, you might be able to find some old sapphire 2 install discs on ebay. You have to make sure its a full install disc's and not a spring update. Also I have noticed that the software itself does not check the hard drives serial# but the install disc's do. Its possible to clone an image of an official hard drive on to a non official hard drive and i noticed some ebay sellers are doing exactly that. Make sure you have an official "MERIT" hard drive by checking in the bios the hard driver should be listed as "MERIT" If not, its not official and the install disc's will not accept it.
They changed this security after 2005.5 force but sapphire 2 was before 2005.5 force.