There are 2 possible reasons for this:
1) Some sort of clogging has occurred:
i) Check if the inlets (beneath the dampers) need cleaning.
ii) Ensure the dampers are clean and well moisturized.
2) Ink Starvation:
Check if the tubes have ink and the ink levels of bottles/tanks.
There is a possibility that you are out of ink.
Please use a very good CMYK test image to determine precisely a possible clog level.
If it is the case that you have already flushed, perhaps the ink is not charged back into the head.
After flushing, you need to damper pulls and hold down the droplet button for several (7 or more) seconds until you hear the pump going.
You can go to the Windows printer section and use the Utility tab in order to do cleanings.
It may take a few cycles to get the ink back into the printhead.
After that keep doing the CMYK calibration prints until you can are all set.