Here are your parts
Replacement parts for General Electric PDW8280J03SS Dishwasher | AppliancePartsPros.com
Here is a manual. It is for newer units but yours should be close.
Could be a number of things:
Dirty filter screen.
Low fill, see Page 24 for where it should be. Often low fill is caused by a dirty inlet filter screen in the water valve. Remove the valve and check/clean it. Do not permanently remove the screen from the valve as it is there to keep crud out of the valve which could hold it open and cause a flood.
Poor seal at the middle spray arm.
Dirt/crud in the pump.
Dirt and debris in the sump. Be care when checking in here as often there is broken glass in the sump.