hydrostatic mower will not move

my daughter has a cub cadet that suddenly decided it did not want to move any more. what is the fix or check out

:welcome:

The very first thing to check is the ID tag under the seat.
take a photo of it and post it here (needs to be off your computer not camera ) .
Once that is done we might have some idea which one of the 352 different Cub Cadets you are talking about.