Digital BW, The Print

Hello, I installed on my Epson 870 the CFS of MIS with MIS VARIABLE 
TONE B&W INKSETS (I have PC with win2k). It worked fine for 2 days, 
but yesterday it doesn't print the black color. I try to clean (with 
3 cycle of cleaning and print a file purge), but it doesn't work.
I try the procedure of MIS for foam and air for two times (yesterday 
and this morning), but I have in the tube of black 4-5 cm of air that 
it shape always.
Can you help me?! It's urgent!

Thank you

Stefano