Mach3 Fresh install and setup on a Win7 - 32bit machine.
Mach3 ver. 3.043.066 DEMO

I am able to jog all 3 axes without issue. 

But get no movement when using STEP or MDI.

Oddly, when I switch between STEP and JOG, MACH3 requires a RESET.

I have a couple machines that use Mach3 and have never had this issue.

Digging around on the NET I found another person who posted the same issue, but no response was given.

Thank you in advance for your response.

If you attach your xml then maybe the issue can be found.
Hood