If the yellow one goes on for 5-7 seconds, then off, and on and repeats forever, that sounds like a "boot loop".
The usual cause of a boot loop is that a configuration change has been made that it can't handle. That may mean something like enabling features that (combined) use too much memory, Feature A doesn't work with Feature B, etc.
(You may try unplugging all extra hardware (GPS, OSD, etc.) from CC3D and trying to boot it then, but I don't give that much chance.)
The easy fix is "Rescue" and while rescuing, combine either:
- "Safe Boot" and set the setting you changed back like it was, while safe booted
- or "Erase Settings"
Go to Firmware page. Unplug CC3D USB if plugged in (power off CC3D till told to do otherwise). Press "Rescue" then plug CC3D into USB. From there both Safe Boot and Erase Settings will be available.