Check your Step and Direction settings

If your motor is “locked” with power applied but they just “twitch” rather than step, then it’s most likely you’ve got your Step and Direction signals backwards coming into the board.
Check your software and compare to the setting in the manual or on the PRO or EZ pages. Reversing Step and Direction will result in the motor twitching randomly as it tries to step on the far less frequent direction signal change.

Check microstepping jumpers

If you have no microstepping jumpers installed (J1, J2, J3) on the 8 pin headers (PRO) or 6 pin headers (EZ), then the motor for that axis will not move – you will be able to turn the motor by hand even with power connected.. You must install the jumpers to enable your desired microstepping. See FAQ Microstepping Configuration.

Verify stepper wiring

It’s easy to get the wiring from the stepper to the board messed-up.  If the steppers whine or twitch, but do not spin, you likely have a wiring mix-up.

Make double-sure you know the wire colors and polarity of your coils, and you’ve got them hooked-up to the right spots on the board. Check the Stepper Motor Wiring FAQ for HobbyCNC stepper motors, as well as a few others.

Did you just move/change your system?

For whatever reason, moving or changing your system is a common cause for things to “just stop working”. Triple-check all wiring, especially the stepper motor wiring.

Check Power

Confirm power switch is on.

Verify fuses not blown.

Visual inspection of all Power Supply wiring – no shorts, no broken wires, no loose connections at terminal blocks, no bad/broken solder connections, any crimped connectors are sound and secure.

Measure voltage at input to board:

PRO (3 or 4 axis)12VDC36VDC42VDC10A (4 axis)
7.5A (3 axis)

IF the steppers lockup when power is applied (even without computer connected) then issue is with computer/parallel port/ cable.  Thousands of boards and minimal (like none) issues with motherboard/parallel port.