If it were me, and as those in the know havent jumped in with erudite direction, Id start with a battery reset.
If you've been tempted by the recent fall in price of 4200s and have been fishing under the seats for a spare quid or two, it may be as simple as a wiring issue if a connector has come adrift.....?
I believe there is a seat specific reset - no idea if it can help in this situation...
4200 seat reset
Unlock the car
Open the door and then immediately flick the seat base switch fore and aft, for and aft (twice)
put the seat back forward
The seat should cycle twice fully forward and fully back then beep (if not you did not flick the seat base switch quickly enough of opening the door)
Put the seat recline back and reset the seat and memory
Repeat for the other front seat.
Assuming none of that has changed the state of play- I gUess you'll have to pull the seat and test the motor on the bench...? I dont think its a massive job.