time for some troubleshooting. do you have a voltmeter? Check the voltage from your power supply to the cnc shield. If you are powering the unit through the black connector on the uno, then you have probably burned up a diode next to the connector, All is not lost as you can power through the blue connector on the cnc shield and this is how it should be done in the first place . Next up, disconnect the cnc shield from the uno and see if the uno will communicate with the computer. If that works, then re-attach the cnc shield and remove the stepper drivers and see if the uno still talks to the computer. Then attach one driver at a time and see what happens. If a driver causes the problem you will need to replace it. You can easily blow a driver if you move the rails and cutter head by hand as the motors then act as a generator and send voltage back down the wires to the drivers. Also "Tis the season" for static and the smallest static shock that you feel is about 5000 volts and the real good snaps with a spark can be 30000-60000volts and you are feeding it into a chip that runs on 3.3volts. The good thing is the electric stuff like the uno and drivers are cheap, the cnc shield is pretty bulletproof as are the stepper drivers. The power supplies generally are switching power supplies and shut down if they find a short circuit. One more thing to check is the speed controller which can be tested by powering directly and using the servo tester to run it. The servo tester can also be used to test the servo but you will have to connect all 3 wires to the tester. Remember that troubleshooting is a bunch of " divide and conquer" and just test one thing at a time. BTW I was a master tech for Konica Minolta copiers and did this ** for 25 years!
