HP6830 won't print

[ChristopherB]

My HP6830 won't print or prints only faded gray portions of files. I did not have this problem the last time I printed with the 6830 about ten days ago.

For example, when trying to print a PDF, instead of the document, I get very faint outlines of the box outlines in the PDF. With printing from Mac Mail, I get only very gray portions of the sending and receiving address. 

At one point I was getting "filter failed" error. I followed HPs online troubleshooting guide to remove the HP software and reinstall. That stopped the filter failed error message but did not change the problem with printing.

[ChristopherB]

On further investigation, the problem appears to be that the black printer head is not printing. The level of the ink in the cartridge appears to be fifty percent. The note to myself is that, perhaps despite the level of ink, something is wrong with the cartridge. I believe my primary choice at this pint is to replace the cartridge and see what happens.

Christopher