Well, if the fan(s) have stopped working, then the only thing to do is replace them.
If the laptop is still under warranty, contact the manufacturer about a repair/replacement. If it isn't under warranty any longer, then you can try and do the work yourself (if you feel comfortable doing it) or you can take it to someone who can do the repair for you.
NOTE: I would also recommend you get the work done sooner rather than later. If you wait, your device will start to seriously overheat and will then cause problems with other components. Not something you want.