HP DeskJet 3755 - faint ink

[cadona004]

I have a HP DeskJet 3755 and the black ink is printing extremely faint and with blank spaces, although there is still about 1/3 of the cartridge remaining. I have physically cleaned the printheads and am now trying to run the clean printheads process through the HP Smart application. I get the screen that says "Cleaning is in process. One page will be printed to show the results of the cleaning." and the gears inside move around for a few seconds. After that, nothing happens. The page never prints and the screen in the HP Smart app doesn't clear, the wheel continues to spin until I click cancel. 

The demo page function worked and the color ink comes out fine, but the black ink will not work at all. 

[GrumpyUnk]

Likely the printer was not used regularly enough to keep the printhead from drying.  Dried ink is plugging the outlets on the printhead.  Remove the black cart by powering on, opening the access door, and pressing downward on the closest edge of the cartridge.  It should sort of pivot.

 Get a paper towel folded to protect ink flow to your fingers, and drizzle a bit of hot water onto the towel.  Use the towel to dab the print head.  It should get black real quick.  Inspect closely to see if there remains more dried ink.  If so, you can soak a bit with the dampened paper towel.  It may take some time to re-liquify the dried ink.  Once you are tired of doing that, replace into the printer and see if it will then print.  You need to be very gentle handling the shiny bits of the printer cart.