Assuming the pump is getting power....
There's a pressure switch mounted on the top of the pump. It's where the two wires with spade terminals connect, and it's held on to the pump body with three screws. If your pressure switch is stuck open, your pump won't kick on. An easy way to test this is to pull the two spade terminals off the pressure switch and then jumper the wires together with a piece of metal. If your pump kicks on, the pressure switch is stuck open. Disassembling it, operating the switch a couple of times, and putting it back together tends to fix the problem. Keep in mind that you'll be opening the water side of your pump, so you'll want to depressurize and drain your plumbing before taking those screws out.