Starting and ECU problems

Help! My Passat doesn’t start. It was sitting in my driveway for a month because I was redoing the interior and I took out the seats. Today I tried to start it and … nothing. The starter was cranking but it didn’t start. I tried to hook up my VAG-COM and the ECU didn’t even register. I am not sure if the starting and ECU problems are related but they might be. Is there a way to find out if the ECU is OK? I have another Passat that uses the same ECU. I am thinking to pull this one out and hook it up to the other car to see if it registers. Is that a good idea? Thanks.

Relay 109?

TDIFAQ

Didn't think of that. I have a spare one. Will try tomorrow. Thanks.

Change the relay 109. Started right away! It almost looked too simple and too good to be true.