Some time ago my arduino shit the bed so I ordered a new one and plugged in the Synthesos gShield v5b and expected everything to work fine but no, the motors wont respond. The Universal Gcode sender responds to the $$ and when I type a command but the motors aren’t spinning. I’ve checked the PSU, the computer, the USB cable and switched arduino 3 times. So I’m out of ideas… Can anyone help me…?
Depending on how your Arduino died, it may have taken the gShield with it.
Check a few things
blue LED on the gShield on with 24 volt power supply on?
When you first bring up power on the Arduino (plug in the USB connector) and turn on the 24 volt power supply do you get three green LEDs lit up on the gShield?
If you move the gantry around manually (with the power off and slowly) do the green LEDs flash?
I have no idea how or why the arduino died, I was playing with the x and y motors and everything worked fine, unplugged everything and put it in a cardboard box for storage and when I plugged it back in the next day it was toast…
Yes the blue light is lit and my PSU is on exactly 24.0 volts.
No there are no green leds when everything is plugged in, but when I move the steppers the green led connected to that axes flashes.
Does that make any sense to you?
Thanks for replying 
but when I move the steppers the green led connected to that axes flashes.
Yes, the motors are acting like generators. It means that at least one of windings in the motor is Ok.
The normal startup with the Arduino/gShield electronics will turn the green LEDs on. During operation the green LEDs with turn on/off/flash and that is normal.
Since the LEDs are not on with a fresh power up cycle it would indicate that the Arduino is not enabling the motors (assuming the gShield is working right).
So, first thing to try is to reload grbl into the Arduino. Make sure that you use the Inventables fork for the .hex file.
Now I’ve tried both the old files and the new, both the hex file and the grblUpload arduino library sketch but still no movement…
If the Arduino seems to be working, (you can upload the grbl code, you can do a $$ command and grbl responds correctly) then most likely the gShield is bad. Contact Inventables support to see if they have any suggestions.