HELP my cello is out of tune totally and The tuning peg wont stay at all?

Ok When I went up stairs to practice my cello the C string was way out tune So I turned the peg up some And I got the right pitch but When I went to use the fine tuners it went all loose again what do I DO? do I tighten the fine tuner a bit or just start with peg and hold the peg and use the fine tuner????????????!!!!!!!!