PLEASE HELP!!!!!!!!

ok guys as all of you know i got my car back. and i know some of you guys are pissed at me cuz i'm selling it. but as much as i dont wanan get rid of it i might have too, but there is a chance i might keep it and get the 99 cobra. my dad said i could keep it if i get it working again. right now it doesn't start it all started when i was driving and my tach stopped working, the speedo. then the other gauges started goin crazy then it started to run like crap and had to rev it to keep it goin. then shortly after it died and know i cant get it started. the interior dome light does not go one when i have my door opened and my windows and door locks dont work. i tryed jumping it with a power box i have and the windows and stuff all works and the car acts like it wants to start but doenst. what could be the problem? could it be the computer? batttery? alternator? i'm lost please help me! thanks guys -Jeff