To test that I slip in a new HDD and quick install/restore the OS. Since a 500GB HDD is now about 50 bucks that's less than half the cost of a service counter encounter.

You can also boot a Live CD/DVD that I noted a few years back. Read http://tips.oncomputers.info/archives2004/0401/2004-Jan-11.htm

There are newer versions but these allow you to look around the OLD HDD if it's still working and get your files out.
Bob