No X axis movement?

Hello I have a orignal mendel with gen3 reprap v1.2 . I have movement from Y and Z but not X, if I plug Y or Z into X it moves fine. The opto end sensors work for Z and Y ,but atm I'm not getting the X one to light up. I even swapped opto ends to see if was the problem but it is not. So question I have is what would make the X port from main board not move the X axis? Not having opto end sensor working?Bad main board? or did I forget something else? So close but yet so far Ty in advance.

Figured it out was weird i swapped the cable from Y with X and now X and Y both work...along with Z. Weird...

You probably have an intermittent connection on one of the ends of that cable. If the connectors use crimped on pins, they may need to be redone. I solder all the pins on my cable ends to make sure they're reliable.

Ty I'll check into what you said.