My car wont starti tried charging my battery, got my starter checked tried to jump start, changed my battery posts and nothing. what can it be? the strange thing is that one day every thing was fine and the next morning it would not start any more.i opened my hood and heard a strange noise by a small fuse box looking thing.

Could be several things. Battery connection, starter solenoid, starter, neutral safety switch, ignition switch. First have someone hit the starter while the key is in the start position. If no start, check to see if voltage is at the starter solenoid. Try moving the gear indicator back and forth from P to D with the key in crank position. Make sure the park brake is set. Make sure the battery cables are clean and tight. There should be several feed wires coming off the positive post. Make sure all are ok. Some are fusible links and may have burnt.

Battery may be bad. Try a jump start. If the engine light is staying on, have the computer scanned and post the trouble codes here.
Do It Yourself Diagnosis and Repair

The alternator would not come into play unless the battery was dead.
Could be corrosion inside one of the battery cables, or a blow maxi fuse for the fuse box. Or a bad ground connection.
You would need to take a meter or test light and check for power at the starter post, and the major fuses.

You can use some tool to check your car. Car Diagnostic Tool

need to check your starter before going to check the sensor.

Check the battery first--turn on the lights--ok? If not, either the battery is dead or the cables to it are in bad condition--usually the connectors themselves. Remove each and clean both post and interior of the connector with a wire brush made for the purpose. If the battery itself is dead, try to recharge it. If it won't charge, you probably need a new battery. If it does take a charge and the truck will run, check the battery voltage with the engine running--you should see roughly 2 volts over the battery rated voltage. If it reads just battery voltage, the alternator probably has problems. An auto parts house will usually check the alternator for free.

Check the battery +12v power connection to the starter is in good order,
Check the ground connection between the battery negative and the engine/starter motor is robust and intact.
If no problem with above, replace the starter motor.

check the starter, start with the wires running to the starter, if everything looks ok remove the starter and have it bench tested.

are the starter motor wires loose?

You should have you altenator checked most local parts stores will do it for free