Almost certainly just a sticky adjuster - there's a good guide somewhere on here to freeing this and I'll go and have a look for you......from memory, in short go into the back seat, get down and pull off the plastic cover at the bottom of the seat and then you can send a socket (13mm?) down the hole and operate the mechanism by hand for a few turns.
Once you get it moving again the motor will be able to operate fine.

Great stuff. Thanks for that.