My Galaxy S 3 stuck on Odin Mode? I wasn't downloading or doing anything?

[Android Question]

I have a Verizon Galaxy S 3, model SCH-1535. It would randomly black screen/powered off while I was using apps. I would take out the battery then just start it again. (This has been going on these past 2 days)
Then today, when I tried to turn it back on after taking the battery out, the screen popped up saying "Downloading... do not turn off target !!" I wasn't downloading anything...

Someone said to hold the volume up button, the home button, and the power button simultaneously. It didn't change anything? Brought me back to the same screen. Even if I power it off and then back on, nothing changes.

Please help! I don't know anything about phones. I wasn't "rooting" or downloading a sofware. (I vaguely understand these terms after googling my problem.)

 

[Rukbat]

It would randomly black screen/powered off while I was using apps. I would take out the battery then just start it again.

That's the point at which you bring it in for repair. It might not make any difference, it might be just the same problem showing up in a different way, but when the phone starts doing crazy things, and you can't find a few "push this, tap that" threads on different forums, all reporting the same fix working, it's time to bring it into the store.