Can you attempt a firmware upgrade? See if it'll talk to the 990.

Check the "OPR - SVC" switch. Perhaps it somehow got switched to the SVC, or perhaps was never quite in OPR in the first place, or is dirty, etc.

Did you *remove* all connections and try powering on? Perhaps there's a fault or short somewhere that you can see, even though all seems like it's correctly hooked up.

Just a few random thoughts.

Good luck.