Why is my Ativ S rebooting contantly?

[WPCentral Question]

Hi!
Earlier today my phone reset spontaneously while I was using a map application. It's called Maps and is made by Live Tiles.. When you ask it for directions, it prompts you to download another app and links you into the app store. I downloaded it. The phone has crashed numerous times, so I didn't think anything of it at first. Then I tried to take a picture and when I hit the shutter button, the phone turned off, I turned it back on, and tried to take the picture again. It turned off again.
After this it started turning off by itself, and then would get to the lock screen, and then turn off again. The window kept getting shorted and shorter. Now it just stays in a perpetual reboot-loop getting as far as the "Samsung" logo, and then going black, vibrating, and starting over again. I have tried factory resetting it several times using the volume/power button combinations, but it always goes back into tis loop.
Interestingly, I was able to get it to the phone setup screen if I plugged it into my computer running the Windows Phone Recovery Tool and catching it in the middle of a boot sequence. I managed to get back into the start screen, but when I launched the camera to test, it went back into its boot loop again and we were back to square one.

 

[SBNaga]

This is the OP again. I had to register to reply in order to "edit" my original post.
So, I just re-flashed my T899M with this: SGH-T899M VLCMK2_R_signed
Using this: WP8 SMD binary USB Downloader Ver. 3.47
The problem persists, even after reflashing. This time I was able to go through the new phone setup, but as soon as it hit the start screen, resetting commenced once again. It is doing the same thing as it was with the 8.1 build loaded: Windows logo -> Samsung logo -> reset -> repeat ad infinitum
In addition, now it also doesn't show up in the binary USB downloader when I plug it in. It shows up in device manager as "USB Downloader", and the connection makes the sound on my PC, but that's all that I can get.
Please, anyone with some advice here would be great. I've moved to Japan recently, and they don't have WP here, so I can't take it in for servicing. It's either fix it at home and keep using my Japanese SIM card, or else buy an Android handset straight out... :/ I really like WP, so I would prefer the first option.
Thanks!