Hi Barbara
I've not read the other posts on this subject so please excuse me if I repeat something that has already been suggested.
I suggest the starting point is to check, using a multimeter, that the 12V supply is getting to the motor. So you need to remove the cover from the motor, connect the multimeter, and press the switch to turn ON the winch. It is important to check the voltage when the winch is connected to the supply as this will also show up any high resistance connections that may be causing the problem. If you can show that you get 12V on the motor terminals then this confirms that you have a problem with the motor. If there is no (or a low) voltage on the motor terminals then you will need to look for a fault in the wiring / connections / switches. If you have demonstrated that the problem lies with the motor itself then all may not be lost. I suggest that you ring round a few companies that repair (or re-wind) electric motors, and take the winch (or motor) to one of them. I live in the Midlands area and Yellow Pages is full of companies that specialise in carrying out this sort of work. I have had several industrial motors repaired and been pleasantly surprised at the cost.
Hope this helps. Good luck.
Chris Bulleid