[Alan Anderson]

What you describe could be caused by wiring two of your motors either backwards or on the wrong side of the robot. If the motors are fighting each other, nothing will move until one of them trips a breaker and the other wins.

Pull all the circuit breakers for the drive motors. Put one in at a time and verify that the motor drives in the direction you expect when you try forward/reverse/left/right commands. Remove that motor's breaker before trying the next one. If a motor consistently turns in the wrong direction, you can either swap its wires on the Jaguar output or toggle the appropriate "Inverted" terminal for that motor on the Open 4 Motor Drive block. If a motor drives properly for left/right but not forward/reverse, it's on the wrong side of the robot and you'll have to find out which PWM cables to swap.

[edit]Based on your Begin code, I think you have PWMs 1 and 4 switched. You obviously duplicated the constants that were already there for the 2 Motor Drive, and that has confused you. The proper order of the PWM definitions is (top to bottom) Rear Left, Rear Right, Front Left, Front Right. Try deleting the PWM and Invert constants, then recreate them individually by right-clicking on the Open function's terminals and choosing Create->Constant from the popup menu. Then right-click on the constant itself and choose Visible Items->Label. They'll get the proper labels attached to them that way.[/edit]