If possible, a video of the full progression from unplugged -> power on -> coin inserted -> machine going crazy would be very helpful, ideally both inside the cabinet and outside (playfield/backbox). Failing that, a clearer step by step description would maybe help. I never worked on a Sonic game and I don't know how they're set up. It sounds like the reset sequence isn't completing -- check all score reel zero-position switches, check switches on reset and/or game-over relays. There also might be some good info found in this thread, in which the problems described resemble your own.