1996 Oldsmobile Cutlass no power at all to anything

for the past month or so, my car has not started at all when i first try to start it. the dash would light up, but when i turned the key to activate the starter, the dash woud go dark and nothing would happen. If i let it sit a while, it would finally start. Now, i get nothing. no dash lights, headlights, interior lights, windows etc. what could be the problem. it acts like there is no battery in the car, but the battery is fine. We replaced the alternator a while ago, go we have done something when we did that?