Hi y'all - help req'd please!!!

I have had my Chinese cnc for a three/four years now and for the light weight work I do it's doing a great job however.......
Because my workshop gets cold (November through to April - in Scotland) I bring the pc and controller into the house when not in use, fire up the heater in my workshop before bringing them back out once the temp inside reaches 15C+. Been doing this since I had horrendous issues with the pc/ cnc machines not working properly in cold temps (below 10C).
Today I decided to do some work. Once the workshop was warm enough, brought out both pc and cnc andplugged everything in.
PC/CNC software (Mach3) fired up okay and is working fine. When I switch on the controller the water pump kicks in and all 3 stepper motors receive power (difficult to move manually).
When I try to move any of the axis using the keyboard keys as normal I can see Mach3 working but there is no movement in the stepper motors
I use windows XP connecting a Dell pc to the controller by means of a 18 pin cable
I have treble checked all connections - XYZ cables, cable from pc to controller but it all seems fine. As mentioned I have been doing this for a number of winters Has anyone come across this issue or is there anything else I can check? I am beginning to think its the cable connecting the pc to the controller as everything else seems to be working

cheers Steve