overheating corsa?

had an accident in my 1.2 corsa and drove it home. it seemed ok. drove it again the next day and seemed ok until i drove it for the second time that day when it started to overheat massivly, would stall when at low revs like slowing down for a corner etc and radiator was leaking. my dad reckons its a broken radiator but i dont get how this could cause stalling and strugglin at low speeds. any ideas whats wrong and costs etc please would be very much appreciated