Blade turns but just pushes grass down

This is most likely that the blade is wrong , going in the wrong direction or is installed upside down. To check this pull the spark plug wire or wires so mower will not start . This is where you might need some help if you can not see the blade or the pulley , crank the engine just enough to see what way the pulley or blade is turning , if you are looking at the pulley it must be the one the blade is attached to. Keep hands clear of all moving parts and wear safety glasses ,remember you are not starting the mower just turning it over to see the direction the blade is turning.The blade should spin in the direction that the sharp edges are facing. When you see what way the blade is traveling it should be with the sharp edges going in the same direction. (sharp edges pointing the way the blade is spinning )Now also on the back of the blade (opposite of the sharp side same end)it should have a slight angle up towards the deck of the mower , this is what pulls the grass up to cut it or mulch it. If the angle is pointed down , the blade is upside down. So it's one of the three . If it's a single blade system , simple wrong blade or upside down. If it's double or three blade could be the same thing or could be that the belt is on wrong around the idler or guide pulleys. Hope this helps you out.