Put the bike up on the kickstand and try handspinning the rear wheel with the key removed.. If you feel mechanical resistance see if the disc brakes are dragging or wheel or tire are rubbing. If the motor doesn't turn the wheel at all, and you have resistance when you spin the motor, something broke internally or you cooked the motor.
I had a similar problem. I unhooked the motor connector and then the motor moved freely again. The problem was that the controller was short circuited. A current is generated by the motor coils each time it is turned by hand, and that current was being fed back to the motor coil through the shorted controller, which causes a magnetic field that pulls on the permanent magnets causing the drag. Unhook the motor connector and see if the wheel spins freely. I then shorted the pins on the motor plug, and duplicated the problem confirming that the controller was shorted out and not the motor. 2nd problem was that the lights were shorting out and the bike would stop when I turned the lights off.. I ripped out all of the light wiring . This bike is one rats nest of wires. The last thing I did was ripped out all the brake motor cutoff switches and wires. Then problem came back, and I opened up the motor and found that the hall sensors were bad, the motor was full of water, after only 10 months of use, the magnets had all fallen off the magnet ring, the one hall sensor was totally shorted out, and the power wires that go into the hub, were worn to bare wire, this was causing the power to short onto the axle and then killing the hall sensors, that in turn fried the controller. What a piece of work this metro is. This bike makes a nice lawn ornament, but is definitely not worth the $4200 I paid for it.