92 Pontiac Firebird won't start

We have a 1992 Firebird that will not start. The problem started a few weeks ago and when you turn the key, nothing, no clicks/grinds, nothing. You can hear the fuel pump kick on but that is about it. When the problem started last time we replaced the alternator and the battery as we knew the alternator was on it's last leg. When this didn't fix the problem we also replaced the starter. Problem solved or so we thought. The car ran great for a few days and then started having issues again. When you turned the key you never knew if it would start or not. If it didn't start you could usually try it a few times and it would eventually start. Now it will not start at all. Any help on what to check next would be greatly appreciated.