Look in the cistern. You should see a long plastic or metal rod which connects to the handle you see on the outside of your toilet. Connected to the rod there should be a chain. The chain should be connected to a round plastic flap at the bottom of the cistern. The chain may have come off the flap or it may have dislodged from the rod at the top.From what you describe it sounds like the chain just came off. If any part of the chain is broken you will probably need to replace the entire chain. If only the hook or the metal ring (which attaches the chain to the rod or the flap ) has broken you can temporarily fix it with a paper clip. Hope this helps.
Erin, January 2007