How do I knw if it's my timing belt or fuel pump car turns over but won't start.

Hello, There are many things that will prevent a vehicle from starting, and while you have listed two of them, make sure that you diagnose the vehicle according to a strategy to minimize guessing. If your timing belt/chain has failed, the engine will not pulse as you turn the key. It will just sound like an electric motor turning, and will turn much faster than normal. It will sound much more smooth while cranking. Also, there will be codes stored for the crankshaft and camshaft position sensors because the engine will not be turning in time with itself. The fuel pump can be heard priming through the rear seat, or underneath the fuel tank. If you do not hear it prime when you open the door or turn the key to "RUN" (one or the other, not both), then you are likely not getting fuel pressure. Check your fuel pump fuse and relay, as well as all of the other fuses to ensure that power will be delivered on demand. Also, you can test the fuel pump by jumping the relay and testing for power/listening at the pump.