The first place I go for a clue as to what is causing a 500 Internal Server Error is to my error logs (found in the logs directory of your user space).
These entries will give you a lot more information as to what caused the error. There is nothing more that we can see by visiting your site unless part of the site runs and then the error message is displayed (we could then at least know what program or process created the error). In the case of your site, we just see the error message with no other clues.
Check those log entries to see exactly what the error is and what file is causing it. Good Luck!