Maybe worn out quick coupler. Possibly coupler is not depressing internal check valve in the fitting. Also, maybe the control lever is not functioning properly. Crossed lines when hooking up can cause implement to raise and not lower (or some other combination failure).
Did you shut off tractor and try moving the control lever through all positions to get blower lowered? If that didn't work and you need to get implement back on ground for further testing, you may need to "crack loose" the fitting. If you do this you want to be aware of the high pressure in the line, and wrap a rag around the fittings to protect from spray, wear protective glasses, and only crack the line a little.
