Hi, My machine (2020) as been sitting in my workshop for around 18months now without doing anything. I have since decided that it has had a long enough rest so decided to fire it up. I am however experiencing various errors like “GRBL Error Homing Failed couldn’t find limit switch” or “Machine controller restarted unexpectedly and may be in an undefined state” ?? Machine was left connected so nothing has really changed since it was last used. Appreciate any thoughts you may have?
Sounds like you may have an issue with the wiring for the limit sensors or the connectors for the sensors.
I would power up the machine but don’t initialize it and check the sensors to see if the red light on the sensor come on. Use your collet wrench and place it on the sensor. the light should illuminate red on the sensor and the indicator light on the control board should also light up.
Red on the sensor = it sensed the object
Blue on the control board (or another color) = the PC board received the signal
If either or both of the lights don’t light up first check all connectors and pins. Place a metal object on the sensor and wiggle each connector one at a time and see if the lights work. Open up each connector and look for pins that have been pushed out or damaged.
Usually it is a connector issue if you do find a bad connector or if you still have a problem contact support@
Hope this helps.
Anthony
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In addition to what @avetrano suggests, fully unplug the power strip from the wall and the machine, same with the USB cable. Let it sit for a while like that, at least 5 or 10 min. The power brick can retain a small charge for a long time, which can cause the board to not fully lose power and reset when you turn off the machine.
While it’s off, check if all the axes move by hand, nothing frozen in place. Inspect your belts, v-wheels, and motor pulleys. Mine sat for a while and the belts took on the stretched shape of the motor pulley, caused some problems. Slipping motor pulley could cause a homing error, check the set screws.
Disconnect and reconnect the motor wire connections at the motors. Then do the same (one at a time) at the board for the motors and limit switches. Sitting “untouched” also means you forgot about the time 12 months ago you bumped against the drag chain while working on another project and jostled a connection loose. 
With all that checked, move all the axes a few inches away from the limit switches, plug in power (not USB yet) and power it on. All the motors should lock, test each to make sure it is firm, no slipping when you push on each axis. If good, power down and plug in the USB, turn on and run your homing sequence.
Still a problem? Try a new USB cable, try a different computer, and try a different gcode sender (gSender, CNCjs, etc.). None of that, could be a bad power brick (there was another post not too long ago about a power surge causing an issue like this, luckily I think it resolved when the power brick sat unplugged overnight), a bad board that got zapped by a power surge, or bad wiring to the limit switches (but the “controller restart error” makes me think it is not the limit switches).
If none of that works, let us know what you find. Any noises, grinding motors, etc.
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