I've used Piezography for years and have a few suggestions. Some may seem obvious, but worth a try.
The first is: What version of Piezography are you using? The new ICC or the Photoshop pluggin?
2) Since it sounds as though you bought the system used, perhaps the ink cart truly IS empty and you need to purchase new ones. That said, it's not a bad idea to purchase replacements anyway, but make sure you aren't using the older formulation and decide to stick in the new ones, You need cleaning carts if that is the case. Also, because the 1280 uses "chipped" carts, there may be a malfunction here and new carts would have you starting from scratch.
3) Take the carts out of the printer, as you would if they were empty and needed replacement, and reinstall/reseat them. The contacts may have become jostled and aren't properly seated.
4) You didn't say what OS you run (XP or Mac), but in the XP driver windoe, there's an option for turning off two-way communication with the printer. This is not really recommended, but might be useful as a trouble shooting setting.
Hope this helps.