Dell Photo AIO 928 (Printer 928)

First of all, sorry if i write something wrong (i'm not english)

I have this Printer with the lastest firmware and software installed on my PC (Windows 7 Professional 64-Bits SO) and i'm having some troubles:

The most important one is that "sometimes" the printer doesnt print a color (Ink Cartridges are Black 51% and Color 72%). It started not printing Black so i changed the cartridge and still had the problem... so i put the first one again. A week later the problem wasnt with Black but with Blue... So i don't know where the problem is.

The second problem is that the little screen the printer has looks like this: 

I'd love if you could help me!!!

Thanks a lot