The number one refilling problem is waiting too long to refill my cartridge. When I don't fill up my cartridge right away, the ink will dry and clog the micro holes at the outlet of the printer head.
This is really a problem of not using it often enough, no? If you keep using it, the head should not dry up.
Are you saying you finish a cartridge then leave it sitting around for a long time before refilling it?
You can try alchocol to dissolve dried ink if it is not dried too much. I have had success couple of times, but if it has been standing for long time I am afraid nothing will help.
Since they are not usable any more You can also try some solvents You have around home but I have not had any luck with them either. Do nor rub print head as You will damage it. Fold several layers of tissue, wet it with alchocol/solvent and put cartidge with print head on it and leave for a while. Keep something disposable under tissue as it might stain under it.
I had this problem several times as I do not print too often. I have noticed that refill inks dry faster and are harder to dissolve then original HP inks. After all I ave given up and bought second hand monochrome laser as I do not really need color.
I jumped on the color laser bandwagon due to this problem. Color laser is $$ upfront, mine was $400 but it didnt need toner for over 1 year, and that was black. Its been over 2 years and I have still not needed to replace color, and this is with 100s of prints and on the crappy beginner cartridges.
Another thought- buy refilled cartridges from e-bay, they come with some kind of frame that seals print heads pressing rubery- foamy thing against them to prevent from drying out and You can use it on your own cartridge when not in use/storage. If You look around you might be able to get just a frame somewhere.
Just shake your cartridge for some time.May be it will start for work and this will work for some time also.And you have to regularly use it otherwise same problem will arise.