My car wouldn't start after I got gas, my dad tightened the battery cables and we thought the problem was fixed. Now, it won't start in general. It's not dead because my radio will turn on.

A car needs 3 things to start: Fuel, Fire (spark) and air (compression.) ________________ FUEL: Check your fuel pump (including the in-tank pump) and injectors. Also, the fuel nozzle, tank. Do you smell gas? Sometimes it could be a fuel pump RELAY that needs replacing. Also, check each fuse in your fuse box, and the ones (you may have) in your Engine. SPARK: Check the spark plugs and wires for good seating, gap, etc. Check the electrolyte levels in each cell of the battery. Go to Autozone and have them do a free battery/alternator test. If the battery is low, they can perform a 'slow charge' on it overnight. ...Of course, IF you can get it started! (It's probably that.) They can also plug in a "reader" to diagnose basic problems. You can buy one of these, too for future use. Check the Red wire from the battery to the starter/solenoid connections, and to the Fuel Pump (under the car.) You may have a FP in the engine too, that may need cleaning, etc. AIR: I have checked all of the above before, and my car still wouldn't start! I called a mechanic, and he took off the Valve Cover, and we cleaned it, filed it flat, and replaced the gasket, and that was it! AIR was the problem. It didn't have enough compression to do the trick. Hope that helps. HINT: With a good troubleshooter, you can avoid most of the above! *Diagnosis is 90% of the cure.

...also, sometimes a battery may turn on accessories (radio, or lights, etc.) but won't have enough juice to crank an engine.