When faced with an engine that won't start, there could be several potential causes. Here are a few things you can look into to troubleshoot the issue:

1. Electrical issues: Check if the battery is fully charged and in good condition. Inspect the battery terminals for corrosion or loose connections. Ensure that the starter motor and ignition system components (such as spark plugs and ignition coils) are working properly.

2. Fuel system problems: Verify that there is enough fuel in the tank. Check for a clogged fuel filter or a malfunctioning fuel pump. Also, ensure that the fuel injectors are delivering fuel to the engine correctly.

3. Ignition system issues: Examine the ignition switch and ignition key for any signs of damage or malfunction. Inspect the distributor (if your vehicle has one) for wear and tear, and make sure it is properly timed.

4. Air intake problems: Inspect the air intake system, including the air filter. A clogged or dirty air filter can restrict airflow and affect the engine's ability to start.

5. Mechanical issues: Check for any visible damage or leaks, such as broken belts, damaged hoses, or cracked engine components. Additionally, consider the condition of the timing belt or chain, as a broken or stretched timing belt/chain can prevent the engine from starting.

If you are unsure about any of these potential issues, it may be best to consult a qualified mechanic for a proper diagnosis and repair. They will have the necessary tools and expertise to diagnose and fix the problem accurately.