Help Me!!!

So i have a 2000 sunfire I just got few months ago. Its makes me so mad so it has been wrecked before. One day It wouldnt start but then couple days later it did and now few months later it wont start at all. It runs good then I turn it off next day when i need to go somewhere i get in my car and wont start. It turns over but it wont start even after waiting a couple days. So I have 3 people telling me 3 different things. My bf says its fuel injectors we even put fuel injector fluid and spark plugs. Keep in mind its not the fuel pump or fuel filter he checked. My dad says its the inertia switch and another person says its the control or im not sure if he said computer but some kind of module. I DONT KNOW???!!! SO I NEED ALL YOUR HELP!!! THANKS ITS GREATLY APPERCIATED!!!

Is there a "theft" light on the dash? If so, observe what it does and then let us know.