Have you adjusted the pots on the drivers?
Are they the same drivers?
Are you sure you have the cables wired correctly?
Is voltage, motors etc... Spec'd to the load?
I don't know your skill level. I hope this does't come across as Captain obvious.
(When i built my MPCNC I used a 5/16-18 threaded rod as the lead screw that caused me nothing but pain. I get these frustrations)
What kind of Cnc are you making?