[T-Mobile, Samsung Galaxy SIII] hesk65426:
To start out, some basic information. I got my SGH-T999 about 2 years ago and used it for about a year on the Stock ROM before proceeding to root the phone. The firmware version before things when went wrong was android 4.1.2. Everything was working fine until about a few days ago when the phone would stop being responsive after putting it into sleep mode, or the screen will turn black and the whole unit is unresponsive (the latter only occurring while I was in the home screen, not while running any apps. Rather, the phone would be fine while an app is running).

Troubleshoot Stage 1

Initialy, I thought there was some sort of app update that was causing this problem, and so I tried uninstalling a few apps that might have been culprits. Didn't work. On occasion, the phone would freeze up while i was trying to uninstall the app. So reading around, someone mentioned that it was possibly the TouchWiz Home that was acting up and I should, clear cache. So I rebooted into recovery (I had the clockworkmod recovery from the initial root). Cleared user data/factory reset as well as clear cache. Didn't work. At this point, the phone was restarting itself almost instantly after booting into the lock screen. I searched a bit more about why this would happen, and came across a post saying that I could be a faulty power button. I actually didn't want to physically alter my phone in any way, so I decided to try to do something with the software first before resorting to altering the physical phone.

Troubleshoot Stage 2

Next thought process was that maybe somehow an OTA was pushed onto my phone and now the firmware is screwed up because of it. So reading through many posts on XDA, I came upon this thread (http://xdaforums.com/showthread.php?t=1771687) for a pre-rooted version of 4.3. I figured, if I was going to re-flash the firmware, I might as well go to the latest one. I proceed to go through the process of flashing the firmware with Odin 1.85, leaving Auto Reboot and F. Reset Time checked. Odin flashes PASS message and I unplug the phone and wait for the reset. Phone starts up all the way past all the logos and to where the home screen was supposed to be. But there was no home screen, just a black screen with only the pull down menu at the top and a message saying "Unfortunately, Settings has stopped working". This message would keep repeating even after pushing the ok button. Next thought process is, maybe TouchWiz is acting up still. So I boot to recovery, reset/format to factory, clear cache, and reboot. Now the phone wont boot past the Samsung logo. Tried to boot to recover again, phone won't boot to recovery anymore. Tried to re-flash the same exact firmware again and this time, odin had some trouble. It would sometimes stop working where it is loading the main code at which point I check the task manager to see if it is still running processes or utilizing any of the computer resources to communicate with the device. I would then have to unplug the phone and reset by removing the battery. This kept occurring about 2 more times before it successfully finished and on doing so, the original problem when I first flashed it was still there.

Troubleshoot Stage 3

Ok, maybe my phone doesn't like the pre-rooted firmware. Looked around XDA again and found this thread (http://xdaforums.com/showthread.php?t=1949687) and downloaded the stock firmware. I stayed with android 4.3 because i read that I can no longer downgrade to a previous android version. Proceeded to flash the Stock firmware 4.3 using Odin 1.85. The process completed on the first try. SUCCESS!! Boot up phone, got past logo, home screen appeared. SUCCESS!! Here, I thought that I was done and my phone was finally working again. So I begin to tweak the settings for my own preferences. I didn't flash anything else or try to root the phone again. I was just plain using the Stock 4.3 firmware that I got from the thread above. After about 10 or so minutes of using the settings, the phone freezes and becomes unresponsive. Won't restart by holding the power button or return to the home screen with the home button. Only other option was to remove the batter and restart the phone. This time, the phone doesnt make it past the Samsung logo screen, and I can no longer boot into recovery. It was stuck on a boot loop and could only be turned off by removing the battery. It didn't occur to me that I should flash Clockworkmod Recovery to reset/format to factory and clear cache as I have read previously and thought that I could just re-flash the stock again. Nope, the same issue came up in Odin as it did with the pre-rooted firmware. Again, I went through the process of checking that Odin was no longer communicating with the phone before unplugging and restarting the procedures to flash the firmware. After about 3 times, the 4th time after unplugging, the screen that tells you "Firmware upgrade encountered an issue, Please select recovery mode in Kies & try again". And when I try to flash again using odin, I get the following message

<ID:0/012> Added!!

<OSM> Enter CS for MD5..

<OSM> Check MD5.. Do not unplug the cable..

<OSM> Please wait..

<OSM> T999UVUENC2_T999TMBENC2_T999UVUENC2_HOME.tar.md5 is valid.

<OSM> Checking MD5 finished Sucessfully..

<OSM> Leave CS..

<ID:0/012> Odin v.3 engine (ID:12)..

<ID:0/012> File analysis..

<ID:0/012> SetupConnection..

<ID:0/012> Initialzation..

<ID:0/012> Get PIT for mapping..

<ID:0/012> There is no PIT partition.

<OSM> All threads completed. (succeed 0 / failed 1)

Troubleshoot Stage 4

New problem! I now no longer have a PIT partition........and reading around, I found this thread (http://www.sammobile.com/forum/showthread.php?t=15719) of someone who has the same error message coming up in Odin. Thus, I found the PIT file via this thread (http://xdaforums.com/showthread.php?t=1848267&page=4) using the link given by DocHoliday77. Downloaded the T999_16GB.pit as the back panel of my phone indicated that the phone was 16GB. I begin trying to flash with Odin 1.85, checking Auto Reboot, re-partition, and F. Reset Time, including the PIT file and using the Stock 4.3 firmware. This didn't work and only came up with the following error message

<ID:0/012> Added!!

<OSM> Enter CS for MD5..

<OSM> Check MD5.. Do not unplug the cable..

<OSM> Please wait..

<OSM> T999UVUENC2_T999TMBENC2_T999UVUENC2_HOME.tar.md5 is valid.

<OSM> Checking MD5 finished Sucessfully..

<OSM> Leave CS..

<ID:0/012> Odin v.3 engine (ID:12)..

<ID:0/012> File analysis..

<ID:0/012> SetupConnection..

<ID:0/012> Initialzation..

<ID:0/012> Set PIT file..

<ID:0/012> DO NOT TURN OFF TARGET!!

<ID:0/012> Complete(Write) operation failed.

<ID:0/012> Added!!

<OSM> All threads completed. (succeed 0 / failed 1)

Tried, the same procedure with the pre-rooted 4.3 firmware, still the same message. And haven't gotten past this point since.

Looking back at what I choose to do to try an fix this shutting down problem, I realize there were a few things I could have tried before moving on. But now what I really want to figure out is whether or not my phone can be saved. What have I not tired and what is the end of end to rescue this phone or if its even worth rescuing. I read that JTAG would be the final resort, and I will take that into consideration. Any feedback on what procedures I could've missed would be great as well (for future reference). Thanks for reading this long post and I really do hope I can get this resolved.