Why won't my pizza cook properly?

Use a proper pizza tray with holes in it or partially cook the dough before you add toppings. You may be adding too many toppings .

The reason might be the heat is too high so it makes the pizza crust and topping black. Keep the heat to the medium so that the pizza cooks completely from inside also. 

Are you putting your oven on broil and not bake? You also might have the temperature set to high.

You didn't set it to the right temperature

Try dropping your oven temperature slightly or lowering your pizza a level or two on your oven rack. You can then bake for longer – try 4 minutes longer – and you should cook your dough through without burning the top.

Maybe, it's not heated well.

Maybe your using too high a heat so the crust gets scorched before the topping / middle is cooked?

Try cooking it on a lower setting for a longer time,, If its 'homemade' maybe you could spread out the topping and leave less 'crust' exposed, hopefully it should cook more evenly. 

Without knowing  your process and pizza recipe very hard to say. either too hot (not really easy to do with a home oven, the lower heat element isn't working so it is broiling or you are cooking frozen pizza at too high a temperature. Again Not knowing what type and process for cooking and type of pizza not clear answer.

Did you coat the pizza stone with cornmeal-to create a bit of space between it and the paddle to give space for air to circulate? What temperature did you cook it at? How long? 

Try not centre loading, turn part way during cooking.