1996 Oldsmobile Ciera Problems

SO about a week ago I was driving and my radio turned off then on. I came to a light and my car died. It started right up. I thought maybe I was low on gas so I filled up(My gas gauge does not work) Then a day or so later I started my car up at work and nothing happened. No lights etc. After about 5 minutese it started up with no problem. Then again a few days later it gave em a little start up problem then was fine. I took it to the car wash to get all the salt off if from winter. Did under body wash. Went to run an errand and when I started my car it started, then idled very high then died. It would crank but not start. 30 minutes later it started up and I drive home. The BF replaced a blown fuse for the lights and replaced a tail light bulb.

This brings me to today. I go to start it. It started then died. It did this two times. Now it wont do anything. No lights, power etc. We are being told by some people who know about cars that its abad connection or wire leading from the battery since its a power thing. The battery tests great on battery tester. So far he has not been able to find the bad ground. So could it be the igntion switch? Starter? Spark plugs? Something else?

Hope you can help me :)