The ink likely has dried in the pipes. Run a little rubbing alcohol through it, then you may need to use a set of cartridges to run the 'clean the heads' routine built into the printer. I've heard some running the head cleaning utility up to 16 times or so before the printer behaved.
The reason being Epson ink is formulated to be very, very resilient. It is not water based, and is designed to last over 80 years in direct sunlight. But since you said you don't use genuine Epson ink, I've no idea what it is formulated as.