severe trouble on 1995 monte carlo Z34
 

well I have a 5th generation monte carlo 1995 Z34 3.4 This week I parked the car and did some work on car like doing exhaust work I had to weld pipes on the exhaust and forgot to disconnect the bty so needless to say for some reason now the car will not start and it backfires and won't start I though I blew the PCM I replaced it and still will not start so I am at a loss for what happened as it was running fine before I did the exhaust qwork. I did not put the resanator back in. Can anyone please advise me I am totally lost.

THanks in advance