Here is a step by step of what JJ is trying to tell you;
Use your "float" position to lower it to the ground.
1.Disconnect 1 hose from rod end of the boom lift cylinder and put it in a bucket to catch the oil if it is working. Then start tractor and move the lever forward (pressure down). If oil comes out that circuit is working, so hook hose back up and go step 3
2. If no oil comes out the hose, trace that line back to the QD on loader valve and remove it. Put a hose in place of the QD, put other end of hose in bucket and try the above test again. If no oil comes out, you have a control valve problem. I oil comes out but did not on step 1, either your male or female QD is blocked.
3. Remove a pivot pin from end of 1 lift cylinder, start the tractor and move stick to raise, extending the cylinder a couple inches. (It will extend without raising the loader unless you hit end of stroke). Follow the line back from base end cylinder to find the QD. Take that QD out put the end in a bucket. Start tractor and try powering down again. If no oil comes out the QD (female or male) is blocked. The QD couplers can stick to stop flow in 1 direction.