Your Profile indicates a 1993 Disco S1 V8....
As you didn't indicate the vehicle in your post I am assuming you are discussing your Disco..!! or have you bought a L322?? Simple deduction suggests this as the Disco, P38 or Classic didn't have power fold mirrors....
I can't see anything in the L322 WSM for the power fold drive system, but I can only assume a linkage has become dislodged somewhere in the drive mechanism...
Can you hear if the motor is turning or is the mirror housing loose and floppy?