A lot of HP AIO printers use two cartridges for ink, one for color, and a separate one for black.
Sounds like your printer is out of black ink, since its printing colors just fine.
To test this, open notepad. Start -> Run: notepad
Type hello and print it, if it turns out blank. then you know for sure.
Also if you have the printers management tools it would show you the ink levels of each color.
Im almost certain that your ink cartridge needs to be replaced (this applies even if your printer only uses a single cartridge)