The first place to start is whether the pellet grill has power and the control panel turns on. If that's not the case, then check the outlet/condition of the cable (any bite marks etc). If the cable/outlet is fine but the control panel still won't turn on then check the fuse on the back of the control panel.

If the control panel has power, then obviously check the hopper has pellets. You'll also want to check that pellets are able to get into the burn pot, as if not, you've got an auger jam that you'll need to clean out.

If pellets are getting into the burn pot but the fire won't ignite then its a hot rod issue, as they do burn out eventually. If the hot rod does need to be replaced, you can manually start the pellet fire with a flame torch, etc, while the pellet grill is running to cover the job of the hot rod igniter.