This might be related to your pcbenv folder but it's unlikely. If you still have the pcbenv_old folder go there and copy the env and allegro.ilinit file to the new pcbenv folder then try again. The Auto-router is only part of OrCAD Professional, Allegro. It's not there with OrCAD Standard.
Can you also try Start - All Programs - Cadence - Release X.XX - PCB Router - Does this start ?