'95 Oldsmobile '88 not starting

[stoopmice]

I have a 1995 Oldsmobile '88 that has several problems. The first noticeable is that it wont start up, the engine cranks but won't start. Also, the power locks and power windows don't work but the radio and lighting does. Added to the power locks when I press the lock/unlock button I can hear a little buzz coming from the doors, guessing the little mechanism is trying but can't.
This is actually the second time this has happened to me, the first time I had it towed to a mechanic and he replaced the connector for my battery's positive terminal since it was corroded and that work fine for about 3 weeks until now. When I checked under the hood, I noticed the part he replaced was rather loose in the terminal so I tightened it, but that obviously didn't fix the problem.
Other things to note I guess would be that both times this has happened the car initially started and I could drive for a bit, then the car would turn off. Now it wont start at as mentioned. Also the mechanic's initial thought was that the connector wasn't able to make a good connection due to all the corrosion which was why he replaced it. And the check engine light does come on when I have the key in.
Any suggestions or ideas as to what could possible be the problem are welcome. Thanks