Need help with sudden lose of upward movement of Z axis during a cut

I am still learning all this... today i was surfacing a board, during the 3rd pass something failed, and the z aixs would only move in the down direction not up... I emergency stopped and started looking at what went wrong..

so i powered the system both computer and controller down and started checking, z axis would only move in down direction when i went to jog it..

i checked the config and nothing changed, i even tried to test move the z axis in the config and same thing only would move down..\

i changed the motor and same thing...

i turned everything off and cursed at it and put it in time out for about 15 min..

i went back out and plugged the z axis connector into the x axis to see if it would work, and sure enough it worked, so i plugged the x axis into the z axis and yup it worked both directions too.

i put everything back together and z axis is moving in both directions..

could someone point me to where i should check to see if it is possible what caused this.. just be for warned i am not really good with computers and even worse with Linux that controls my controller..

PS.. i was making deeper passes on the surfacing cut than i have ever done before, is it possible the system over heated?

Is this a pc computer issue or
A cnc controller issue???

I am using a probitix cnc controller and there pc system, it uses Ubuntu linuxcnc and no way of updating the system, it has no internet connection

I would check the cable to the Z dir on the driver for a break. If it happens again check the voltage on the dir connection when you jog it up and down as it should be about 5v in one direction and 0v in the other.

i checked the voltage as it was easier to get to, at the back if the computer i get 5 v in one direction and in the other direction it goes to 0..

i checked with the cable on to make sure no break in the cable and same reading..

so now i need to check the cable on the driver... i have been using the cnc for a couple of months now and never had a problem... the only thing i did different today was i was cutting at a deeper z depth when surfacing than i have ever done, i was cutting 1/8 and i could hear the router struggle with the 1 1/4 cutting bit.. could i have put to much pressure on the z axis and it over heated or just freaked out to hold the position

Maybe you fixed it when you unplugged and switched the z and x motor cables. I have found it isn't unusual for a plug to have a bad contact. You should check those plug contacts for signs of arking.

Again this forum and the experience here is great, thank you all for always helping out...

So i took the recommendations and dug into things on the cnc machine..

i checked the voltage and it was ok

The CNC Controller (probotix cnc controller) i have had this for several years, this is not a jab at them,, I went through all the wires in the controller and found not several but a lot of loose wires, I made sure they were tight and put it all back together..

then lastly because i have a probotix computer system also, and i had been trying to ad some programs to get a joystick to work, and thought maybe since its a closed system and no internet access maybe i downloaded something that was interfering..Probotix offers a download of a reload of ubuntu and it cleans everything else off..
i did the computer download and re configured Linux ..

i cut the same exact piece i was working on the other day when it failed, and no errors or fails today..

again thank you to all the help i get here.

Are there screw terminal connectors involved?
It is possible to have the screws tight on rising-clamp terminals, with the wire loose underneath the clamp. And then you can get effects like this. So check that each wire is tight as well as that the screws are tight.