have you done any tinkering inside the printer lately? have you noticed any degredation in your prints/nozzletests before this started?
start from scratch: clean everything. always helps to have a good starting point and cleanliness is half of the battle. capping station/wiper/printheads, run a 99min nozzle wash, before trying another nozzle test print, and run another nozzle wash again before another test print, in hopes of signs of recovery.
then down the rabbit-hole you go:
line of diagnosis is to start with determining if the issue is above or below the printhead, and it sound like if your capping station is still drawing ink through the waste lines then your ink supply should be fine and the pumps/capping station are working properly. leaving you with the printhead and electrical/communications above. extremely rare to have all printheads stop firing at once, so what do they have in common? ribbon cables to slider board, and from slider board to main board you may have some misconnections or crimps in the cable inhibiting communication, encoder strip issues across whole length is unlikely but an encoder sensor could have dust/debris/ink build-up inhibiting the sensor reading. Easy to remove & inspect, but clean carefullly as its an optical sensor, or simply replace to easily rule-out.
....oooor you could have done something crazy like fiddle with your dampers lately, dripping ink down all of your ribbon cables into all of your printhead electronics, frying all heads in one-shot. Printer still recognizes them being installed, but communications during printing are permenantly bungled.
which has happened plenty around these parts and easily overlooked as people rarely assume they broke their own printer while trying to run service on consumable parts, or are simply in a line of thinking while trying to service one issue, but ruin another part of the printer in the meantime and keep thinking that the original issue had just simply gotten worse.
