It sounds LIKE you have SOME code on IT that BLOCKS the CLOUD connection, which causes IT to go into BREATHING green. That is EXPECTED behaviour, and most LIKELY a RESULT of your CODE.
NOT being able TO erase credentials MIGHT also have SOMETHING to do with your CODE.
An ERROR descriptions would HAVE been very NICE. Saying it doesn't WORK isn't too DESCRIPTIVE, and HARD to debug. Does the CLI give you an ERROR? What do the LEDs do?
READ a TUTORIAL? SEARCH the COMMUNITY? BROWSE some TOPICS? Let ME save you the EFFORT:
Because that is the DEFAULT behaviour. If you want to CONNECT over SERIAL using the CLI, then you SHOULD use the CORRECT command: particle serial wifi, rather than particle setup.
Also, WHAT is 'LITERALLY NOT HAPPENING'? Again, an ACTUAL description of the ERRORS would be more HELPFUL than 'it DOESN'T work'.
THERE are VARIOUS topics on this on the COMMUNITY, as well as some HELPER tools, one of WHICH I just LINKED you to.
Also, you CAN'T 'just INCLUDE' things in YOUR random program that MAY have been LICENCED.
Once YOU have the CLI and DFU-UTIL installed, you SHOULD be able to do particle flash --usb firmware.bin. So FIRST try to get THOSE up and running.
In the short term, go with @ScruffR's suggestion. Place the device in safe mode and try setting it up again. Once that's successful, I'm going to assume it goes breathing cyan, and then breathing green again. If that happens, place it in safe mode again, and once it's breathing magenta, try flashing 'blink an LED' or 'tinker' to it. See if it then stays breathing cyan.
WASN'T that much MORE pleasant to READ than with all THOSE random CAPITALIZATIONS ;)?