This guide will give you an over view of how to clean the heads in a typical inkjet printer. I have tried to make the guide as generic as possible and the tips should work for most printers.
The process documented here is considered risky at best by many experts but if your print head is so dirty that no amount of head cleaning via the built in mechanism works you have got very little to lose by giving this a shot.
First thing to do is get the top off which can be easier said than done. This printer had four screws holding the top on as shown in the two images below.
After that remove the control panel by undoing the four screws holding it in place. This isn't strictly necessary but it makes life easier.
Now move the print head to the left. To do this you have to lower a locking bar that is located at the base of the head. The head can be quite hard to move but it does slide left.
Unfortunatly, at this point I stopped taking photographs because the job was getting messy but I can talk you through the test of the procedure.
Under the print heads you will find two pads of hard foam. These collect the ink when you perform a normal head clean and keep the print head moist. Mine, along with the print head itself, had dried out. Soak these with water - I mean really soak them. Pool water on them and let it run through (it goes through to a large pad at the bottom of the machine by the way).
Fold some tissue and lay it on the base when the heads pass over. Push the head back and forth over the tissue to clean the actual head. The tissue will come out covered in ink.
Now for the tricky part. Get an old printer cartridge and remove the label on top that says "do not remove". Under the label you will find a couple of holes. Widen them / open them with a drill bit about 3 mm is good. Fill the cartridge with water and put it in the printer. Push the heads back over to the right as far as they will go. This will cause the sponges to come right up against the heads. Leave the set up over night.
In the morning test the printer. Mine had all but one or two heads unblocked. Run a couple of head cleans with the cleaning cartridge in. I found that the printer would print for a few pages then give up. I repeated the over night standing and after 3 nights the machine printed perfectly.
The most interesting result from this exercise is the quality of hte print from my ad-hoc testing cartridge. It's as good if not better than a real cartridge. I will probably start refilling all my cartridges with water from now on to double their life.