zanussi tce7124w condensor dryer won't stay on?

My Zanussi condenser drier will not stay on longer than 30 seconds and sometimes not at all. It will start then the light says the water container is full despite being empty or the green light, i think it's supposed to mean the clothes are dry because it used to stop automatically, comes on despite the clothes being wet. I would really appreciate any help on this, I'm a student, so if I can't fix it myself it's going to stay broken! Thanks