What would make my Mtd 30 riding lawn mower start but won't drive could it be drive belt?

Absolutely

Your shift rod is not seated properly.

The shift rod is attached to your transmission at the rear wheel,

right by the brake pads. There is an adjustment nut for the shift there.

1. Loosen the nut but do not remove it.

2. Manually put shift in Neutral.

3 Now tighten nut.

4. Shift should now be in proper alignment.

5. If this does not work, try again. You will see that by

pulling in and out on the short shift stub coming out of the transmission,

that this is what you need to adjust.