When the machine is in E-Stop condition, the encoder feed-back should still display on the screen. Check the connections between the encoder and the X Axis connector. When everything is good, you should be able to spin the motor (encoder) and see the DRO value change.
I've replaced the X axis cables many times, especially on machines with seal-tite. The X cables are the only ones that move and flex. Over time, coolant can harden the insulation, the seal-tite will crack, and coolant and chips will get inside. The chips can cut through the insulation and cause short circuits. Milltronics has also used a 'composite cable' here. These get hard and stiff and can have broken conductors inside.
Sometimes, you need to replace the seal-tite and/or the cables.