DIAGNOSIS A pellet feed jam. Moisture-swollen pellets or fines (sawdust) are clogging the auger tube.
FIX Turn off and unplug the grill. Empty the pellet hopper completely. Use a shop vac to suck out any remaining pellets from the hopper throat. Use a long, flexible brush (a clean bottle brush works) to manually clear the auger tube through the hopper opening. Refill with fresh, dry hardwood pellets.
IF THAT DIDN'T WORK The auger motor itself may have failed. You can test by removing the hopper and watching if the auger turns when you start a cook cycle. If it doesn't hum and turn, the motor needs replacement.
HEADS UP Always store pellets in a sealed, dry container. Never leave them in the hopper exposed to humidity for long periods. Damp pellets swell and are the primary cause of jams.