2000 cav flickering problem need help

Hey, last night I was helping a buddy with his car and when i went to go home i put my key in the ignition and when i turned it, it started clicking similar to a battery being low. so, i took my voltmeter out and check the battery. looked good. i also noticed when i turned the key taht the lights on the gauges started flickering as well as the dome light. i had him put jumped cables on me and it happened to start right up. i drove home, and this morning my car wouldnt start again, same problem. cehcked batt. voltage checked good at 12.6. i tried to have my gf jump my car but it didnt work at all. ive never seen this problem before and i would really really appreciate any ideas that anyone reading this may have.
thanks,
Bryan

just wondering if u found out what was wrong with the cavy i have a 2002 and it is doing the same thing, interior were lights dimming and flickering and now it made a sound of it shorting out and nothing seems to be working at all, but all the lights on dash are lit and stay lit even with key off. battery checks good and it doesn't sound like an alternator, please help if you have any answers, thanx, AJ

blairaj02@sbcglobal.net