Powerbook G4 - menu bar keeps freezing

We inherited my father-in-laws Powerbook G4 17" with the latest OS. I believe it is a 1.67MHz processor with 1 GB of ram. When a few applications run simultaneously, the menu bar freezes up and we can't do anything unless we know the keyboard shortcuts. We can sill start and switch between programs using the Dock, but that's it. My wife took it to our local WeFixMacs store and the dude said that the HD needed to be replaced. Is there a way for me to check at home without buying a new HD and installing? Also, is there a way to install a new HD if we don't have the original install discs? Im much more of a DIYer, but I don't know a whole lot about Macs yet as I'm a recent convert.