My motors shake

Hi there.

I have this setup: arduino mega connected to my cnc controller - straigh to the parallel step-dir pins.

I have this problem - when pressing on 100+ (or 10+.. etc) on repsnapper, or trying to turn on the extruder (both regular and reverse) - my motors always spin to one direction (I disabled to limit option).

Can this be due to ground which wasn't connected from my cnc controller (link)?

the motor spins for about a minute before it stop....

will appreciate any help here.