I'd bin it personally. It sounds like the head that reads data isn't working properly. This can be exchanged from an identical hard drive but as people have said, it needs to be done in a specially dust free environment (no mr muscle will help you here!). If you get the slightest spec of dust in there, you're knackered anyway. With prices being so cheap, i'd just treat myself to a new drive :)
Ben
March 2008