I am assuming lgt2654 is a hydrostatic drive , you mentioned if you push your foot down or backward while engine is running the tractor does not move , turn engine off before checking belts etc
Firstly might pay to check the drive belt is still on the rear Trans pulley and the front pto pulley, and the belt has good tension on it and is in condition, and while clutch brake is in the off position, check brake is not stuck on.
if you have had wheels off for some reason, be sure the square keys are back in the wheel hubs if your wheel hubs have non captured keys., or you will have no drive , be sure that fwd /reverse link rod is connected and moving the Trans arm (which moves the swash plate) @rear transmission causing pump to move oil to motor which turns differential unit then turns axle /wheel assy , if this is OK then could possibly be low oil in transmission or Trans fault