Pool has been sitting for 9 months. Where do I start?

Came into a house that has a pool that has been sitting 9 months with only 1-3 feet of water in it.  Live in SC inground, vinyl liner, Grecian, DE Filter, composite type base behine liner.

Liner obviously needs to be replaced.   However, our concern is the equipment.  How do we check the pump, pipes and DE filter?

You could briefly turn on the pump and see if it starts working. If it runs, it should be ok. The filter can be opened up and the grids can be checked for holes or other damage. Some of this stuff won’t be known until the liner is replaced and water is in the pool. At that point, you can test everything else in the system.