A4983 driver not producing output, except when output is shorted to GND
Your shunt resistors R10 and R12 appear to be way too big.  Therefore the device is always in current-limit.

Read pages 7 and 8 of the datasheet, use Ohm's law as suggested.  Also make sure to calculate the power rating on the sense resistors.

Also, pay attention to voltages on the SENSEx and REF pins: