The problem is likely either the alternator or something else preventing the engine from firing. Here's how to distinguish:
* Check the battery: A weak or dead battery can cause the engine to crank slowly, but still turn over. Have the battery tested at an auto parts store to ensure it's holding a proper charge. A weak battery *might* crank the engine over, but won't have the power to get the car to start.
* Listen for unusual noises: While cranking, does the engine sound weak or hesitant? Are there any unusual clicking sounds? These could indicate issues with the ignition system (coil, distributor, etc.)
* Check for obvious fuel delivery problems: Can you smell fuel? Does the fuel pump prime when you turn the key to the "on" position (before cranking)? If you can't smell fuel and/or the fuel pump doesn't prime, there is no fuel being delivered to the engine. This would be a more likely culprit than the alternator initially.
* The alternator's role (a subtle one): The alternator *doesn't* directly contribute to starting the engine. Its job is to recharge the battery *while* the engine is running. A bad alternator won't stop the engine from starting (initially), but it *will* prevent the battery from recharging. This means the car might start but won't stay running for very long if the battery is weak. A properly running battery could still get you started, however, so this wouldn't be the first thing to check.
In short: If your Cutlass Calais turns over but won't start, the problem is much more likely to be fuel delivery (fuel pump, filter, injectors), ignition system issues (spark plugs, wires, distributor, coil), or a weak battery than a bad alternator. Focus your troubleshooting efforts on those areas first. Only if you've ruled them out should you suspect a problem with the charging system (alternator or wiring).
