I have two full ink cartridges but with both the cartridges I've got the same issue -while printing the printer prints all sentences properly except that the lower 50% of all the sentences isn't printing at all. It can't be a problem of ink shortage since I've got enough ink in the cartridge.
Should I clean up the print-head since I see it getting covered up ink or should I try buying new cartridges ?

Extra info: I'm only using a black cartridge for grey-scale printing, I'm not using cyan magenta or yellow cartridges.