I've got a HP C4780 printer which I have had for around a year but only used about 5 or 6 times! Despite the ink cartridges having ink in them, the black cartridge is not printing at all. Not even a smidging. I've tried the usual cleaning processes through the HP solution centre, but nothing is making it work Please help!!

What could have happen was that you refilled it when it was emptied dry, usually this spoils the cartridge. I would recommend you buy a new one and when its about 80% empty that's the time to refill, not after.

INK PROBLEM
Inkjet printers need to be used frequently to prevent inkdrying out and blocking the print head nozzles.
If the print head cleaning maintenance routine does not clear the blockages,then print head needs replacing, but it may be expensive.
It may be more cost effective to buy a later model and better printer thanreplace the print head.

Yes it could be the problem. Try and get a different print cartridge and if it doesn't work you may just have to get a new printer.

Did you replace the cartridge with brand new one? or refilled one?

I'm assuming that your cartridge head may be clogged by ink.....

If you have a refill tool, you can do some stuctioning job....if you don't have one..

Pure some water in paper cup (prefre warm watter) and then leave your cartridge for 20 min to resolve the clogging probelm

And take out your cartridge from water.... and wipe out the head.... and put them back to printer.

If you would like to save money, try refill kit by "ROADINK".
Not only they are easy, but also the printing quality is good.
For your better understanding pls check out my youtube video.
And will see how easy ink refill can be done.

http://www.youtube.com/watch?v=tZlkJ-YDsZA

Hi there!
You will see the cartridges once you open the front cover. Here's what you can do to check on your cartridges.
-Make sure the printer is on. -Open the front cover, the cartridge should automatically move towards the center. You will notice a pink and a black top cartridge and also instructions on how to replace cartridge on the cartridge door.
Hope this helps!

some ink cartridges you can't re-fill....

You may have a dud. Try using the cartridge in another printer of the same model. Otherwise return it to the store and have them test it or exchange it for another one.

Ok. As per your statement , the power cable is working properly. So , the problem is with your printer only. If you are using the original cartridges and still having the priblem , it is only the defualt printer. If you are having the extended warnty for (3) years , you are adviced to contact ' HP Authorised Service Partner'. they will replace your old printer with new one. Generally the HP company is giving 1 OR 2 years warranty for replacement.If have paid extra amount for extended warranty , your printer may have warranty up to (3) years. So, within the period of (3), the HP Authorised Service Center will replace your printer. They will give reciept for your old printer, and replace your prionter within a (15) days to (25) days with new one. If the printer is not having warranty or extended warranty , the printer is assumed to be as damaged. So, you have to purchage the new one. Be, cuacious the HP printers are not repairable. Please don't try to approach the local repairer.They will eat your money and also don't try to purchase very very very costly HP in cartridges. I think your problem may be solved.

Switch off the printer and switch on again,Unclip the cartridges one by one and clip back in again this sometimes cleans out the connector pins.This has happened to me.

> won't accept

Error-messages? What happens? What does not happen?

Did you refill the ink-cartridges yourself, or did you take it to a company that does the refilling?