Trash your Phase One prefs (in the User/Library/Preferences/com.phaseone.captureone.plist)
Disconnect all your external FireWire devices and you camera and relaunch C1 5. Does that allow a normal start? Quite, connect your camera and restart C1 5, does it start and see the camera? If so, quit and restart with the camera and the FW drives connected...that work?