Been there. Common BX problem. Center o-ring in steering cylinder is flat-spotted allowing hyd. fluid to just run through. Cylinder needs to be rebuilt or replaced. Do a search and you'll find bunches of discussions.
Went out today to figure out how to fix it and it is working fine now. No idea when it will quit again. I will need to get it fixed before the snow flies as I will need it to keep the drive clean.