Try turning off the computer as well as the printer when you refill.
HP's are finicky about refilling, they tend to get air bubbles in the sponge. I gave up after a few years and started buying my refills at Cartridge World for about half price. See if there's a store near you, because DIY refilling is unreliable.
Keep 2 blacks and 2 color cartridges, so it's never an emergency when you run out.