You'll probably get much more help if you post this in the Galaxy S3 forum:
http://forums.androidcentral.com/sprint-galaxy-s-iii/
What, if anything, did you do to the phone before this started happening? Did you root, or try to root, the phone? Were you trying to install a new ROM? If so, which one. Did you install any new apps just before this began?
What have you tried to do to remedy it? If you haven't already, remove the battery, leave it out for a few minutes, and put it back in. Do you have an SD card? If so, take it out and try to reboot.
If those thing don't work, can you boot into recovery mode? Turn the phone OFF, and wait until it completely shuts down. Press and hold, at the same time, the volume UP, home and power buttons. When (if) you see the Samsung logo, release all three buttons. What happens?
Facebook
Twitter
Instagram