ok well first off i need the full model and serial number before i can give any decent help on this.
Other than the usual checks for good connections, make sure no fuses are blown.
One suggestion is to check the power at the CR48 relay, this relay turns on when you pull out the estop and have the key turned on, this relay powers on the ecm and platform box (depending on what positon the key switch is turned, the ecm should power on either way. According to the diagram in the service book it is the relay located closest to the tilt sensor. It may be labeled as such.
Check your estop switches and mounts for those switches and make sure they are seated properly and the switches are actually turning on/off like they should. Also make sure all your connections from the key switch are good, wiring to the ecm as well. Check the red wire (terminal 2 & 4 jumpered), from the key switch to the CR48 relay and make sure there is power on it at the ecm connection.
Also there is an orange wire (terminal 1) from the key switch to the ecm to check the same way. Terminal B and B1 (jumpered) from the key switch supply power to the estop switch #2 terminal, this supplies power to the 7Amp motor controller circuit breaker terminal. Terminal 3 is for the up/down control so you can ignore that for now.

If you still have the old ecm check the part number on it to the one you currently have installed and make sure they are the same part number.