Are you logged in under an administrator user or a regular user?
Sounds like a permissions problem. Try logging in as an Administrator (or root if you have it enabled) and then try to start it. If that works, then there's a real permissions problem somewhere, and someone else who has a little more *nix experience may be able to help you.
However, if that doesn't work, then you may have some totally different problem, which we can try to figure out later.