Hi. I've been looking for a solution to this very same problem, but I think that the only way to fix it is to replace the print head. I've spent a few hours now trying to find out if there is something else which could cause this problem, and the only one that applies to me (and to you, if you replaced all of your ink cartridges), is that the print head is no longer working. I found a print head for $50 at http://www.precisionroller.com/k_canon_i560_print_head/m114d5908c104/ , so I'll probably go that route.
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