1. Soak the misbehaving ink cartridge in a cup of HOT water with a few drops of dish soap in the water.
2.. After 15 minutes take the cartridge out of the water and run the fingerprint part of your finger over the bottom (ink production spot) of the cartridge.
3. With the bottom down shake the cartridge into the sink with a "whip cracking" motion until there are streaks of ink appearing in the bottom of the sink. (Picture that the microscopic ink jet holes are plugged with dried ink boogers and you are shaking them out.)
4. Take 5 paper towels, fold them into a square the size of a dishwashing sponge. Now wet the towels, sopping wet. If you get two parallel lines of ink or a small rectangle you have achieved your objective. If you don't get any ink, you have a no good cartridge - you should probably throw it away. If you get partial lines with small breaks, the breaks show you that some holes are still plugged and you may get printing, but it will have white streaks in it.
5. Put the cartridge back into the plotter and test.
I'm an expert with the older HP Designjet functions, repairs and drivers. If you have a question, call me. Answers are free...but I do charge $50 for remote screen driver loading -- but I don't charge until you are printing. Yes, I can get your older HP Designjet to work with Windows 10. Don't waste another minute screwing around with it. Call me. Susan, The Plotter Princess 651-247-3022