What could be wrong with my self drive mower it does not drive thanks?

There are many questions that need to be answered before this can be answered.

- is this mower one that drives it self or is a ride on

- what is the trade name and year of manufacture of the mower.

- Is it chain drive , friction drive , belt or hydraulic drive or any other

The main thing is you have established that is the drive system that is At Fault and when you know what type of drive system you have, it will highlight where the fault may be