Based on the information you have provided, and without being there to check out your printer myself, I can't know what is causing all of your ink channels to suddenly not print, but I can give you a little guidance to help troubleshoot (and hopefully resolve) your problem.
I just re-read our communication above, and have a question- you originally wrote that you had the C and LK Epson carts installed, and all others were the refill carts. At that time only the two Epson carts were printing. I asked you to check a few things with the refill carts, then you had a LM chip issue, which I offered to send you a replacement chip for, but you decided to get an Epson cartridge instead of waiting for a new chip to arrive. The next thing you reported is you installed a set of Epson carts and still have a "completely blank" nozzle check, are you saying that now all 8 channels, including the C and LK are not printing at all?
The things that could cause all channels to suddenly stop printing are:
1. Cartridges (though it would be impossible for all your refill carts to be defective, and are having the same results with Epson carts).
2. Air in the ink lines- if the refill carts weren't primed correctly prior to installing into your printer, then air could be drawn into the ink lines, which would interrupt ink flow when it reaches the dampers and print head. If this were the case, you would have had to install all the refill carts without priming first, and done cleaning cycles or made several prints for the air to travel to the dampers and interrupt the ink flow. You would not see the effects of air immediately after installing the refill carts, as it takes time to reach the dampers. If air is causing your problem, you could check the internal ink lines to see if they are filled with ink, or have air inside- and if you see air, do a few power clean cycles or an initial fill cycle to purge the ink and fill the lines with ink again, which should resume ink flow to all channels.
3. The dampers are a few years old, clogged with particle build up and need to be replaced; though it would be unheard of for all 8 dampers to totally clog at the same time, as the M + Y channels are usually the first to start showing signs of restricted flow first, then get progressively worse, followed by the other channels. I have never heard of 1. a damper suddenly/completely clogging when the channel was printing fine right before, or 2. all 8 dampers suddenly clogging at the same time. Dampers should be replaced every 1-3 years to keep the print head clean and maintain good ink flow, we have replacement dampers, and again- you can replace them by following the repair manual.
4. The pump has gone and needs to be replaced. In these printers, there is a pump under the capping station (sold as one unit, called the "pump cap assembly"), and an air pressure pump behind the left bay. I have replaced both of these parts myself with our 9800, found them both pretty quick/easy by following the repair manual, and ordered parts from CompassMicro.com. If there is no air pressure, there is no ink flow- this would certainly effect all channels at once.
5. The print head is suddenly/completely clogged in all channels (HIGHLY unlikely since you said it was working well just recently).
6. Electrical malfunction- of the print head cable, main board, etc... This would cause the printer to act like it's printing, and could even have good ink flow thru the print head during cleaning cycles, but absolutely no nozzles from any channels fire when printing a nozzle check or image.
Please note, I am not a certified Epson tech, but I have worked with/on many Epson printers ranging from small desktop to large Pro models over the past +/- 10 years, and have maintained/serviced all our production studio printers for about 6 years, so have learned a great deal about how they work, and how to troubleshoot problems. I am able to provide advice from my experience, based on information a customer provides, but can not guarantee anything, and can only provide advice based on my experience/knowledge. There is still a lot about printers that I don't know, because I haven't been formally trained, but am constantly working on and investigating our various printer models to learn more about how they work and how to repair them yourself (we haven't had to call a tech in several years, and have saved $thousands servicing our own printers over the years).
I feel like many repairs can be done by the user, depending on the user's technical skill and comfort levels, provided they carefully follow the repair manual, allow plenty of time (don't rush), and pay close attention to what their doing. Most repairs can be done with a few basic tools, and repairing your own printer will both save you a ton of $ and give you huge satisfaction and pride after successful fixing your machine
Things to consider before deciding to work on your printer or calling an Epson tech are: how much time you have to work on the printer, and how quickly you need it fixed, depending on the problem- what are the possible causes, how much $ you're willing to spend, and if you have the ability to read and follow instructions. After reviewing the repair procedure to see what's involved, checking the costs of parts, and deciding how much time you have to work with, you will determine if it's best to call a tech or if you want to try it yourself (this is especially more appealing if the printer is older/out of warranty, and you're looking at $1,000+ to have a repair tech come in). Also, depending on the severity of the problem, possible causes, and costs involved, some people decide it's more economical to purchase a new printer with a warranty instead of spending $ on an old model, which is likely to have more issues to come. My perspective is it's usually worth trying to fix it yourself, before calling and spending a bunch of $ on a repair tech, or buying a whole new printer.
Please keep me posted, I am curious about your strange problem, and would love to 1. hear of your success, and 2. know the solution to your unusual issue.
I hope this helps, all the best~ Dana