Car Won't start now.

Hello, I have a 1990 Chevy Corsica that has 165,000 miles on it and has a 3.1 liter engine. Here is my situation. At first, the turning signal on the front right side was not working and then the lights on the dashboard that are displayed, when the turning signal is activated, stays on. I talked to some experts and they informed me to have my flasher bulb replaced and so I did. I also checked all the fuses and replaced all the bulbs in the headlights and and tail lights. Then, we took it for a drive to town when all of a sudden, the speedometer showed 70 as we were going around a corner at realisticly 25 - 30 mph, I first noticed the vent was not giving any air, then the car died out and came to a stop. I replaced the alternator and battery within the last 3 months and both the alternator and the battery showed strong charges. The next day, I turned the key to see if it would start and it did. Two days, later and to this day about a month later, it won't even click when I turn over the ignition.
What could be the problem. Is it a computer shortage or something electrical?
thanks for your response.