1998 Chevy Blazer Electrical Problem (death)

Three times I have tried to start my 98 Blazer and it is totally electrically dead. If I disconnect and reconnect the battery it then works fine. The battery is new. The first time was with and old battery. The next two times with the a new battery. It does not die while running. The first time it happened I had had a key made which did not work and the electronics died while trying to use the key. The other times were unrelated and with origional key that works. Any Help appreciated.