This sounds like the valves are not in the correct place. Each valve is numbered and also numbered on the outer casing as well. There is a corresponding number on the valve and that needs to be facing you in the playing position as you insert, just a slight turn of the valve and you can feel it move into the internal groove. It now should go down and screw it in. Repeat this process with the other valves. Finally blow air through the instrument if it is free you’re O K. If not back track as one of the valves is not in correctly.
Unless there is something stuck in the instrument this solution should work. If you are still having trouble take to your trusted instrument repairer or music store.