Went to turn on shower and nothing happened - - you can not hear any running water and nothing comes out? It is a one handle faucet and no bathtub. I took the cap off the handle and tightened the screw and that didn't do anything? Any other suggestions -- could the faucet just be bad?

Does the sink and toilet still function propertly? So far what you did has only made the handle tighter, has nothing to do with the function of the faucet. Tell us about your valve, one handle or two, pull out and twist or what?