Stepper motors sputtering

[the_0utsid]

I have hobbycnc 4axis with 400oz steppers, using Mach3 on win xp.
I set up the board and did a successfull test run before putting the board\power supply in a case.
This weekend, i installed the steppers on a small mill and did some jogging and to my surprise there is a sputter. I got down to where i removed 1 stepper from the mill and the stand alone motor still sputters.
The computer i tested the board on was a Win95 but the pc running the mill is xp.

Can anybody tell me something obvious that i need to to to eliminate the sputtering?

TIA

[Fastest1]

You say it worked correctly prior to installing the steppers on the machine? You removed 1 stepper and it still misbehaved? Were the others still connected to the wiring and the machine? Back to square one, remove all steppers and test off of the machine. Do they work correctly now? Is your cable shielded? Do you have the drain tied down at both ends? Gibs too tight?