hotpoint freezer FZA30 stopped working?

this model has always suffered from buildup of ice even though it is 'self defrosting'. I took the back panel (inside) off to defrost. Freezer will not start again. No damage was done. changed plug fuse. checked wall socket. Only thing i have noticed is the small slotted temperature control on the front does not seem to have any resistance. it is about ten years old. Any ideas?

johnny
February 2015