HP Photosmart 6520 will not print

[DSB_2]

My HP Photosmart 6520 has stopped printing black ink.  The paper outputs from the printer, but only extremely light shadow image appears, so much so that the paper appears blank.  Based on support articles, the following has been tried:

• New black cartridge installed.  (previous one was not empty)
• Other color cartridges are fully depleted, so 'black ink only' under 'print in grayscale' selected (as stated in manual).  Plus for a long time I have printed only using black ink with no problems.
• Driver uninstalled and new driver installed
• Ink cartridge vents checked and appear OK
• Clean printhead utility performed numerous times
• Attempted to run Print Quality Diagnostic Page but nothing is shown
• HP Print and Scan Doctor installed and run

None of these actions had any effect on the output.  Any help would be appreciated!

[Johnharper241]

Printhead cleaning is the most effective solution for unsatisfactory prints, especially streaky or missing black or colors. Use a Print Quality Diagnostic report to check if the printhead needs to be cleaned or if there is an ink cartridge alignment issue. Load plain white paper in the tray.

[DSB_2]

The Print Quality Diagnostic report comes out blank.  By printhead cleaning, do you mean the process:

• From the printer control panel, open the Setup menu.
• Open the Printer Maintenance menu.
• If necessary, open the Tools menu, and then touch Clean Printhead.

I have run this several times to no effect.  If there is another process to clean the printhead, please advise.