If that is the only LED on (other than the power on LED), remove the
cartridge and take a good look at the contacts on both the cartridge and
within the printer carriage area. If other LEDS are on, or blinking,
that is an error condition and a code to tell you what's up.
There are several wires in the printer that need to contact the pads on
the chip on the cartridge. These wires are made of a brittle gold
plated wire, and should they get damaged, dirty (with ink , etc), or
broken off (they are brittle enough that if roughly handled, bent or
abused they will literally break off.
If they have broken, I believe MIS is now offering replacment modules.
If they are bent incorrectly (they shoudl be fairly evenly spaced, VERY
CAREFULLY adjust them with a small screwdriver or similar tool.
If they are dirty, take a cotton swab and using some ammoniated window
cleaner or isopropyl alcohol, gently clean them and let dry, then wip
ethe pads on teh cartrideg itself with a clean paper towel, and
reinsert, making sure to get the cartridge firmly in place.
Usually, that will fix it. If not, sometimes 3rd party ink cartridegs
or counterfeits will not work, occasionally Epson will have a batch of
badly programed chips.
If you refilled this cartridge after it read empty, and did not
reprogram the chip with an Epson cartridge resetter, the printer will
consider this cartridge empty until it is reset.
Art