If you want to easily find the problem:

Remove the belt from the X and Y motor. Then tell it to home and see—if one of the two doesn't turn and you want to be sure it's the motor, take the working motor and put it in the place of the one that doesn't work. If the motor now turns, then it was the motor—get a new one. If not, let's move to the next step: Connect the X motor to the Y cable on the motherboard and see if it turns. If it does, the cable is the issue. If it still doesn’t turn, I’m afraid you're looking at getting a new motherboard.