Help Stuck in Boot loop! Need Help!

[PlateMan]

I found my spare Samsung G S3 and it had worked just fine. But when I went back to it a week later it would only get to the splash screen showing Samsung Galaxy SIII but then the screen would go black. It would vibrate again and do it again in a boot loop.

I looked everywhere online and I factory reset it and cleared cache partitions but yet still does the same thing.

I've heard of Kies and such but nobody has been able to explain it to me. I'm really going out on a limb here and I need anything that can help. Any suggestions????

 

[Madbat]

Which s3 do you have? Which carrier?
Kies is a program you put on your PC. I use kies3. Google search it will be one of the first results. Install it on PC then plug in your phone.
Or if you download the firmware for your phone you can use Odin to install it.