How to fix Samsung Galaxy S3 to boot successfully?

I'm using *Samsung Galaxy S3 GT-I9300*. Recently, I installed an app and the problem started. The phone started to crash. I had to restart the phone to work but the problem just repeated. But now, when I want to boot the phone, it just shows me the Samsung animating logo with a blue LED light, but it doesn't boot successfully and stays on showing the logo. I tried many times to wipe the factory data, but nothing is fixed. Please tell me what to do.