[curtis73]

alternators, batteries, and starters are all interconnected in diagnosis. So many times when a battery is found to be defective and gets replaced, the problem returns. Often times a bad battery causes the alternator to work too hard and it dies as well. Vice versa, if an alternator dies and lets the battery go dead it can ruin the battery. When a starter goes bad, it can make you think that the battery or alternator is dying. It will turn very slowly and sound like a dead battery even if its not. This in turn taxes the battery and alternator. A problem with one of these components can create a problem with the other two. Since you've replaced the battery and alternator, I suggest trying the starter next. Since you said the lights come on but it doesn't start, I suggest that the starter is taking a vacation.

Before you do that, borrow or buy a test light or a multimeter. The meter is preferrable. Remove the negative cable from the battery and put the meter (set on amps) between the cable and the battery post. If you get more than about 0.2 amps, you have a drain. Something in your system is shorted out and draining the battery when the key is off. Start pulling fuses one by one until that meter reads less than 0.1 amps. (Don't pull the radio fuse; its supposed to draw some to hold station memory)