Kossel - Printer ignores commands, motors don't move

I'm running Repetier under Pronterface on a RAMPS 1.4 control board.

Using the 'home all axes' button on the control interface in pronterface causes the printer to home all axes upwards and verify, as expected.
Therefore, all the motors, endstops etc are correctly wired and functioning. I have checked baudrates, which are 115200

Trouble is the printer ignores all commands sent via the command line. The output is as follows:

">>> G91
SENDING:G91
ok 0
>>> G1 Z-20
SENDING:G1 Z-20
ok 0
X:0.00 Y:0.00 Z:120.00 E:0.00"

The same issues happen in Repetier-Host.

1) It always responds to home commands sent via the interface,
2) It never responds to axis movement commands sent via the interface
3) It never responds to any commands sent via the command line (except if you send a command before homing, and then only M codes not G codes)

Repetier-Host gives timeout errors occasionally but these problems happen regardless

What have I forgotten to check?

A few things I would try:

You say you use the "home all axes" button in Pronterface's control panel. How does the printer respond if you send it G28 via the console?

Does the machine move when clicking the motion buttons in Pronterface?

Have you tried using absolute positioning (G90) rather than relative positioning (G91)?

If you have a controller display, does it work with M117 commands?

What does it do if you send it an M302 and a G1 Exxx command? (try running the extruder motor, in other words)?

Have you tried heating the extruder or bed?

Hello there, thank you so much for your reply
This problem is getting really frustrating!

1) Printer doesn't respond to G28 via the console

2) Machine doesn't move when I click the motion buttons (this is the core problem)

3) Absolute and relative positioning make no difference

4) No controller display

5) The extruder motor doesn't turn either

6) Hot or cold extruder doesn't make a difference, and the bed is not installed at the moment

It will home a few times, when I send the commands, then will just stop responding. The first few times I send M119 get endstop status it will respond, but not after that
Also, it never moves when I click the motion buttons

I have tried it with a different Arduino and have had no luck. Any ideas?
Thanks again!

The only other things i can think of to try are different baud rates, a different USB cable, different host software, and different firmware.

How about a different operating system? Plugged it into my Linux Mint laptop and after a bit of installing software, the printer runs well!
Now to calibrate it.

Thank you for your suggestions.

Do you have the jumpers on the pins under the stepper drivers? don't laugh, heaps of people do it and it has the same symptoms you describe

There are no pins, just flat pads (not drilled through), joined with solder. It's working in 1/16th microstep mode (160 steps per unit with 20-tooth pulleys and GT2 belt)

Good old Linux Mint. My choice of everyday OS these days.