My 1998 Lumina won't start

Today I went into the store (was gone for 20-30 minutes) I came back out and my car wouldn't start. As I tried to get it to start I noticed that the power locks didn't work anymore either. Then someone tried to help me jump the car and it refused to start it would only make a clicking sound. After about 15 minutes after we stopped trying that the power locks wouldn't work again and it wouldn't even make the clicking noise.

I replaces the alternator just last year about this same time.

Does anyone have any ideas what this could be.

Bad battery connections, dead battery, leave the car running and jumper cables on for 10 minutes then try it.