Adding onto what Scott has said about spacing being key and looking at the RF utilization. Have you surveyed the area? This is the best way to "see" the impact of the other APs, from there you will at least have an idea of what you are trying to work...
Here's a link to a document that explains, among other things the meaning of each LED sequence, just search for "Checking the LEDs" in this document if you want to quickly find the relevant section: https://www.cisco.com/c/en/us/td/docs/wireless/acce...
That LED sequence is an indication of insufficient inline power. So it sounds like the AP isn't getting enough power to enable it's radios. Is it powered from the switch or a power injector?
