It's been so long now that I don't quite remember but I once did a similar thing in hooking a pc power supply. I crossed the 5V and 12V lines.
I wrote the whole machine off as dead. I lost my CSA Derringer 030 and several other things. It was a sad day. I later found that by replacing all the socketed chips the machine fired right back up again.
If you manage to get a hold of some replacement chips (like Agnus, Denise, etc...) you may be able to get it up and running again. Whether it's worth it or not is up to you since it may not solve your problems.
