If a toyota camry won' t start but makes a buzzing noise, what needs to be checked?

A buzzing noise when You're trying to start Your vehicle -- including the Toyota Camry -- Your issue most likely resides with Your battery. While there are a number of ways these might fail, You're typically looking at either an old battery incapable of holding a charge, a failed alternator, or a component that's drawing power while Your Camry is off. A good firSTStep is to check the voltage of Your battery with a digital multimeter, so You know how to proceed -- You won't want to waste good money on a replacement battery if Yours is still functional. Try to isolate any components that could be drawing power, like a light that won't turn off. If You can replace these, Your car should be on its way to as good as new.