I'm sorry to hear that your LK cartridge isn't working. After reviewing your order history, I see you recently purchased refillable carts for your Epson 4900.
Does the cartridge lock into the printer correctly? If so, it may be a dead chip battery or faulty chip, in which case we'll send you a new chip and battery. Information for replacing the chip on a 4900 refill cart can be found in the cartridge instructions, and info for replacing the chip battery can be found here: http://www.inkjetmall.com/wordpress/product-use/r3000-cartridge-batteries/
Please let me know your results after changing the battery and/or chip, if you have questions, or there's anything else I can help you with.
Best regards~ Dana