Spindle won't run using mach 3

Hi All, I'd be grateful if someone could offer some advice. I have a Denford Microrouter Converted to use Mach 3. I did not do the conversion and I have lost the contact numbers for the guy that done it for me, so I'm abit stuck at the moment. I have very basic knowledge of mach 3, however it was all setup and running before so I'm not sure what has changed now. When I use the MDI screen and enter M3 S20000 I hear the relay turn on but the spindle does not. I have checked the obvious like the safety switch and spindle switched on with no luck. I have also plugged the motor into the mains directly and it works fine.
I'm hoping someone else has experienced the same and look forward to your replies. Thanks in advance Ryan.