99 chevy lumina completely dead?

I have a 1999 Chevy Lumina, 3.8L model-

Just recently, about 2 weeks ago, i purchased a brand new battery from sears auto, and put it into my car. Last night i went to start my car, and the lights on the dash lit up for not even a second, then nothing. I got no turnover whatsoever, nothing. NO response electrically, no matter what i did turning the key. I checked fuses, didn't find anything, so my friend eventually jumped me- My car started, so i drove it home. Once i got home, i went to lock my doors, and had no electrical response whatsoever. I had just driven 5 miles home.

So basically, i was wondering if anyone had any ideas as to what the culprit could be? Car compltetely dead, no response- friend jumps car, car drives, once i kill engine, no electrical.

ALSO, i put my interior light on while driving, and it was flickering, as was all the lights on my dash.

Thanks in advance for any input/ideas- i know i will have to take it to a mechanic no matter what, but i just wanted to get some info first-

-watchinfaith