I have a old baitcast reel and it is  a EX500  , I think it is. Quantum. And the tension knob does not work! I can move the tension all the way tight and the bait still falls like  I had no tension on at all. Is this something that I can fix or is it shot?

Should be easy fix if you can get the replacement part.  I'd call Quantum with the model number of your reel and order the part from them or just get the part number from them and order the part on ebay.  There is really only a small number of things that could be wrong and any of them should be cheap and quick to replace.

You've likely lost one or more spacers from the cap. Should be easy enough.