Galaxy S5 stuck in downloading..do not turn off target , says could not do normal boot. What can I do to fix this?

[lutej]

galaxy S5 stuck in downloading...do not turn off target , says could not do normal boot

my galaxy s5 screen went black then message that "could not do normal boot" and a large green android appeared with message that it is downloading do no turn off target but no movement. after several hours with no change I removed the battery and used the volume up,home and power key to get to the recovery screen. I have tried to clear cache partition and reboot system but after I select reboot system now the phone shuts off and I am unable to power on unless I remove the battery again then I am back to the same "could not do normal boot" downloading...Do not turn off target screen. what can I do to fix this?