Hop particles can plug a keg. Release the keg pressure with the relief valve. Take off the out post, pull the dip tube. Make sure the dip tube is clear, a dip tube brush is something you should have as it works well clearing obstructions. Then look at the post and poppet upside down. If it is green in there, you need to get the hops out by pressing out the poppet, cleaning, and pressing the poppet back into the post. Then sanitize and reassemble the dip tube and post on the keg. I have done this in the past.
If you had the in and out switched, they can be terrible to get off. If they were not bad getting off, I would get out the wrench.