I experienced something similar with a club member's Atlas MP15-DC. The decoder locked up with absolutely no response even on the club's NCE PowerCab based programming track. I couldn't do a reset. I took the loco home and, using the QSI Programmer with Q1a upgrade "inquiry button", was able to 'resurrect' the decoder. N.B. the QSI CV Manager was not able to bring the decoder back to life. Without actually upgrading the decoder, only using the Q1a upgrade software worked.
The sound, lights etc., came back and the decoder worked. However, in this case, every time the loco was throttled up, the loco might move briefly until the current draw tripped the short circuit protection. The likely cause is a motor winding broke and the entire motor needs replacing. A motor with a broken winding will work sometimes if the armature is rotated to access the working winding.
Do you have access to a QSI Programmer?