Ender 3 Z Axis stops moving after printing roughly 20 layers

I have an Ender 3 that will print perfectly the first 15-20 layers and then not print any higher, but still extrude. I can manually move it it’s full range of movement in the controls, but it won’t complete a print higher that 3/4” tall. I was wondering if anyone had an idea of what it cost be or how to fix it? Thank you.