Yeah the check valve should be in the closed position except when draining, so that's not your problem.  Experts should be showing up here with things to troubleshoot.

As long as you're down there, you can replace the check valve with a currently available GE part that will fit.  Spray arm action can be compromised when the valve doesn't close anymore. I may be able to locate the part number if I do some digging and if nobody else posts it here.

Disconnect the hose from the drain connection under the sink to check if the connection is plugged with grease buildup, etc.  A friend had this problem because she did not operate her dishwasher often enough.  The grease eventually hardened and plugged the drain connection completely.  I cleaned out the connection, reattached the drain hose and voila, the dishwasher was draining again. 

Gary

The KD 21 DWs had very few drain pump problems as the drain pump impeller is made of SS and is very durable. Assuming that the drain hose from the CV is clear it is possible that a piece of broken glass, metal, bone etc is stuck in the outlet of the drain pump housing, which will require the pump to be dissembled and inspected.