Are you able to enter DFU Mode again?
Breathing white usually would indicate your firmware is using SYSTEM_MODE(MANUAL) or WiFi.off(), but the factory firmware should not do that - unless you had once replaced the factory image.
To revert back to the real factory image try this
particle flash --factory tinker
And then perform another factory reset.
You can also follow the steps in this thread
[Spark core] Common issues
And make sure you’re using the most recent CLI.