Ok.... So from here we need to check the motor itself:
From the manual:
Error Code 425
After start is pressed, the tread belt does not move and then "Err 425" appears. To reset this error code you must unplug the treadmill from
the wall outlet for 10 seconds, and then check the items listed below.
Check the drive motor wire connection to the power supply.
Check the ceramic fuse (20 Amp – 250 V) on the power supply.
So you have done the fuse so check the drive motor connections, un plug and reconnect...
If no luck then we need to test the motor:
# get a 12-18 volt dc battery fully charged(like one from a cordless drill)
# Make sure it is fully charged, because it won't work if not
# attach the + and - to the motor red is + and black is -
# If the motor turns slowly your motor is ok, if not the motor is bad and would need replaced
# if the motor is ok then your power supply is bad and needs replaced.