i jus bought my cavalier it ran when i changed brakes it ran when pulled it out it quit and wont start what could it be

Your fuel pump in the tank is shot. Take off fuel cap. Put your ear to the hole as someone turns the key to Accessory. Do you hear the pump humming? If not, check your fuses and fuel pump relay. If they look good, replace fuel pump.

i have excelllant fuel pressure all the way threw to th injectors its like they arent opening up? reset the anti theft and replaced injectors

I heard if the oil pressure sending unit is bad, the car will not fire up. Have you tried putting the gear shifter to N then see if it starts? You may just have a bad neutral safety switch.

i have tried putting it in neutral im resetting th computer now thought that would cause it but i will try that next thanks had another mechanic say it could b the heat sensor

it was running i drove it about 50 feet and it quit

Heat sensor? Usually if it's anything to do with the temp sending sensors, the car will always start when cold. It's when it gets to operating temp that the car will usually quit because the faulty sensor is sending signals to the computer saying that the engine is still cold when in fact it's hot. That causes too much fuel to be dumped and the engine stalls. I don't think it's a heat sensor issue. Sounds like a fuel delivery issue. I bet it's something to do with anti theft.

ok ill try that again thanks again its got me stumped