Xperia Blog submitted a new resource: Xperia C5 Ultra_E5506_29.1.A.0.101_Latin America_Generic - Sony Xperia C5 Ultra (E5506) Android 5.1 firmware - Generic Latin America Read more about this resource...
help! when flahear with flashtool cell was left dead and no longer on! stays with the red light and the computer recognizes it as an unknown device. not enter fasboot (Volume -)
Try keeping the phone charged for a while, and then do a hard reset to see if that makes a difference. You can also try holding down volume up +power key combination.