[GregR]

I'd recommend calling an electrician. There are a dozen reasons why a light might not turn ON, but not being able to turn a light OFF, especially one that was previously working fine could be a significant safety hazard like a short circuit or major, dangerous mis-wiring like like having a hot neutral. If you don't know what the problem is, don't risk burning your house down by relying on a public message board instead of a professional.