Lost front wheel drive

[bfr44]

Any help would be welcome, I've seemed to loose the front wheel drive on my 96 foreman 400. I have blocked it up and spin the rear wheels and the front will not spin. If I pull the front shaft backward it seems to engage the front wheels. I don't know if it has broken a key or something. I have taken off the front diff cap and the gears seem to look fine. I hope its an easy fix. Any help would be greatfull.
Hunter