Have you checked the Epson website for guidance? The tech support on most major printer manufacturer sites is usually pretty good. You aren't using refilled cartridges, are you? Sometimes those wont' work because the cartridges the manufacturer use have an ID chip on them that tells the printer it's a genuine printer cartridge and not a knock-off cartridge. Forces people to only use genuine printer cartridges from the manufacturer.
Off the top of my head, I'd recommend taking out the cartridges. Turn the printer off and unplug it and let it sit for five minutes or so. Then, put the cartridges back in. Plug it in again, and then turn it on. Might just need a reset like that to get the sensors to recognize the cartridges. If that doesn't work, start looking at the Epson site to see if you can find that particular problem for your model of printer and whether they have a recommended fix for it.
jag