I did a pretty good thread with photos of striping and servicing my KingOne TDS winch.
Clicky/Linky
http://www.landcruiserclub.net/forums/showthread.php/49681-Servicing-my-TDS-9-5-Winch
As Chris says though, start at the beginning and move forwards;
Is the battery good?
Is the connection to the battery good?
Are the crimped terminals sound?
Is the isolator working correctly? Mine recently failed and has now been completely removed!
Is the contactor in good working order? Again these can sound as though they are working, but if the contacts are burnt the winch will not run! I've also experienced this and is why I now use the TG Thompson contactor.
Are the connections to the motor sound?
Even if not under load there is a lot of amps flowing and it's surprising how the most innocuous thing can halt this flow!
Here's some photos of my original Durite style contactor in bits. You can see the black carbonation damage caused to the contacts from arching when under load and the discoloration also caused from running very hot also causing some of the plastic components to have melted due to the heat build up! There is also some green corrosion due to some moisture ingress. All of this had conspired to stop the winch working even though the contactor was still clicking in and out.
After a good clean up and putting it all back together without replacing any components for new she worked a treat. I had to increase the IP level with some DUCK tape though as she had a few cracks in her body and some large bits missing!!!
NB - Just remembered that my M8 Mog had some troubles with his almost brand new winch that had had no real use and had only been on the truck for a very short period of time. During a fairly intense 4Hrs of winching his winch started to become intermittent clicking on and off ultimately completely stopping!!! This turned out to be corrosion in the motor housing due to water ingress that had prevented the brushes from moving freely in the housings and becoming disconnected from the motor segments, stopping the winch from working!