2002 Pontiac Grand Prix Starting

Electrical problem
2002 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic

40th year anniversery edition 2002 Pontac Grand Prix. Will not start--battery dead. Changed alternator and battery. Alternator is putting out 14.54 volts to battery when running. Battery was charged up full and checked out by store where I bought it. The car set there for three weeks and startted just fine. So apparantley nothing is drawing down the battery. It ran good the first day, was shut off about three or four times and started just fine. Came home parked started just fine the next morning stopped and started twice and quit. Very low battery again and would not jump from other auto with jumper cables again.
Just could not get any kind of spark when connectiing jumper cables. When trying to start after about 15 minutes was hard to get dash lights on with key on, but when did get them, stepping on the brake caused the fuel gage to quit working and started to drop down to empty. I think there is some kind or type of starting relay that may be bad or causing a bad ground. One other time this happened and all the lights on the vehicle were going on and off in rapid succesion just before it started the last time. Any reccomendations.