been a while on a 2000, but here goes.
You need to check for voltage at the switch, probably 24VDC, but I can't remember if it's a negative 24 or +24 that goes to the I/O board. No prints here.
Also, check the switch in MDI mode, by turning on coolant or something. Sometimes a interlock from a spindle or chuck clamp, or turret will cause the cycle start not to work. Barfeeders are very common to do this as well. Check all the connectors on the boards as well, they get fuz around them causing weird problems.