That has a Hydro Gear 314-0510 for those that can help.

might start by checking some of the simpler items - such as missing rear axle key(s) due to a tire change/repair; a frozen up brake caliper mechanism (located on the tranny's housing); a badly stretched ground drive belt; a damaged driven pulley on the tranny (usually also involves the tranny cooling fan).
Checking the latter of these is best done with the deck removed and using a troublelight. Consult your owner's manual for detailed illustrations/adjustments/etc.; use rattlecan brake cleaner to free up a frozen brake caliper. Observe movement of tranny speed control linkage for any problems - clean/lube as needed.
Good luck.

I would remove the deck and have a look at the traction belt and pulleys. It could be simple as the belt popped of an idler pulley. Verify that both wheel keys are in place which lock the wheel to the axle. Start simple.