96 Chevrolet Lumina

96 Chevy Lumina, 169,000, v6

When I try to start my car, sometimes it takes 2/3 tries to either get it running or to keep it running. It's trying to start every time, but just can't get enough power to fully start/ for some reason stay on. Runs pretty well once on. Also, the seat belt light never goes off now and the radio only comes on some of the time. It just puzzles me because sometimes it doesn't come on at all, sometimes takes like 5 minutes and sometimes comes on right away. The radio never goes off once it's on, except on the next time I turn the car on. It's especially touchy on turning on if the car's been running for a while, gets turned off and then turned back on. Then it hardly ever comes back on at all. What's going on?