Start with simple and look under the tractor to see if anything obvious is broken. Then go next step of raising front tires off the ground and spinning them by hand. Do They turn smoothly or rough. Any clunking or erratic movement Would point towards gear or bearing failure in the drive train. If locked in front wheel assist and one front tire on the ground will the other one turn?
jd 5115m , Ford 545D, Kubota M8540, NH t4.105 , Ford 5030, Ford 4830, NH TN 95FA, Volvo EC60E
I don’t know for sure if you’re 7040 has a electric solenoid that engages your fwd but if it does that would be the first thing I’d check. See if it’s getting power when you throw the fwd switch, if it’s got power see if you can hear it click on and/or put your hand on it and you should feel it click on