The problem is that air has got into the spike where the carts would normally sit and dried the ink in the head. This will be very difficult to soften and will take much perseverance on your part.
Get a syringe and some ammoniated cleaning solution or cartridge flush. You get cartridge flush off ebay - I use the JR brand, but that is my personal preference.
Remove the ink cartridges. Take some kitchen paper and fold it up so you can lay it in the bottom of the cartridge carrier leaving the wicks (The spikes upon which the cartridges sit) accessible.
Take the syringe and fill it with the cleaning solution. With a torch look closely and notice the small holes in the top of the wicks. You are going to flush out these wicks with your cleaning solution and the needle of your syringe.
Push the needle of the syringe into the hole of the wick. DO NOT APPLY ANY PRESSURE when inserting the needle. Use no more than the weight of the loaded syringe. Once inserted, SLOWLY depress the plunger of the syringe to ejecta few ML's into the wick. Do this for each wick and then leave the machine for at least an hour.
Repeat this several times replacing the kitchen paper each time you do it. When the cleaning solution starts to run clean you can start to eject the fluid with a little more speed to wash it further into the head. Again leave for an hour each time. Once you are sure you have dissolved as much ink as you are ever going to, you should proceed to do an intensive under head cleaning as per my previous post HERE
. Also put a good amount of cleaning solution into the pump cap (the bit under the head when it is in the park position) and top it up as it seeps away.
Once that is complete and you are again sure you will not get it any cleaner, get a full set of brand new and GENUINE cartridges. DO NOT be tempted to use cheap compatible cartridges for this maintenance exercise. Put the new carts in and allow the machine to charge the ink. Keep an eye on the pump cap and keep topping it up with cleaning solution. If the solution does not get sucked out of the pump cap, then you have a further problem and you should let me know here so I can help you sort that.
Print a nozzle check and see how it looks. If it still shows some gaps, run a couple of cleaning cycles via the button panel and print another check pattern. If there is little improvement after a couple of cleaning cycles do another manual under head cleaning.
You will eventually get the print back. For future reference, if you are leaving the machine unused for a while - leave it with full genuine ink carts. The genuine carts have an anti coagulant that helps to stop the ink solidifying in the head.
Let me know how you get on