Thanks Mister Micawber, there is another thing I would like to know. Is "help" in the sense used in my second sentence always in singular form ? For example, if "you guys" is my subject should I say "You guys were a great help" or "You guys were great help" ? Can we use the form "helps" as plural of "help" ?
It's usually 'you guys were a great help', but I have heard some people say 'you guys were great helps'. It is, after all, a very casual utterance, and needn't stand on grammar.