Need Help! B5100 Hydraulic Diverter Valve

I have had the B5100 with Loader for a few months now and love it. Have
learned a great deal from this great site! Have owners and shop manuals.
Understand use of knob under seat to switch hydraulics from loader to three
point. Purchased a 36 inch tiller that works great. I know that tractor can
only run three point lift or loader but not both at once. Have switched between loader and three point several times in the past few months. Now for the problem. When I switch diverter valve under seat to run loader with lift select lever in lift position and start tractor, lift select lever moves to neutral and screeches. No loader hydraulics. Stop tractor turn knob to three point, start
tractor and rear three point hydraulics work great. So basically have no hydraulics to loader. Any ideas on things I could check? Is the Diverter knob
and valve possibly the problem? How hard is it to remove? Appears in parts
manual to have several O rings. Would greatly appreciate hearing from anyone
that has insight on this. Thanks

Wolfman, Thanks so much for your reply. I had overlooked the obvious! The
loader has a quick connect on the line coming out of the tractor. It sets right by the four wheel drive lever. I was in two wheel drive and this lever is very close to the quick connect and had pulled the connection apart enough that flow was restricted. Learn something new every day.