I'm not exactly sure what your problem is, but it is probably one of the following:
CLOGGED PRINT HEAD
I usually remove the print head (I believe on your device this requires taking the printer apart and removing the carriage) and soak it in rubbing alcohol. I then use Qtips with rubbing alcohol to clean all of the remaining ink-paths that exist in the printer. It's messy but usually cleans out a clogged head.
CARTRIDGE ISN'T BEING VENTED
First off, make sure that the little piece of plastic covering the vent hole is completely removed. On some models there are multiple holes being covered and it's easy to only pull the cover off of the first one or two. In an extreme case, I've used a small drill bit to create my own vent hole that I knew for certain was open.
According to this blog, there is an ink-level sensor on your device that might be malfunctioning or otherwise be in need of bypassing. Something to check.
DATA CABLE NOT WORKING
Each print head has a data cable going to it and sometimes they break or get unplugged. If you're getting no black printing whatsoever and the problem is none of the above, take the device apart and verify all the connections. Unplug and replug any connectors that are related to this system - or just be thorough and replug every connector in the entire machine. Oxidation can build up between pins over time and this simple task can fix the problem in many cases.