Samsung S3 stuck on samsung logo? Sometimes my lock screen would show but can't unlock it?

[Yuukina Tomoko]

Hi I have a samsung s3 and it keeps on restarting and stuck on samsung logo. Sometimes my lock screen would show up but when I try to swipe and unlock it, it won't. Nothing happens, and after that it would go back to the samsung logo. It was working fine in the morning. I put it away in the afternoon to save some battery but when I try to use it, my lock screen won't let me swipe and unlock it. And then it restarted and is now stuck on samsung logo. I tried to take out the battery and put it back after a few seconds but all it does is the samsung logo problem. HELP.