Stuck in APX mode won't boot or turn on / charge - any fix yet?
TL;DR: Any way to fix/flash a Nexus 7 that reports it's in APX mode to Windows yet, that won't do anything else?
I've had a 2012 Nexus 7 32gb since the day it came out (Oct 2012 or so?). Worked great for a year, loved it! Had AOKP on it, unlocked/rooted, used tons of apps, never a single problem. And then one day while I was using it to play music while charging it, out of the blue, it hard shut off while it was running, rebooted and shut off during boot and... never turned on again. Wouldn't indicate a charge, wouldn't turn on, couldn't get it to respond to any power or volume key presses, nothing.
I called Asus, and they agreed it needed to be repaired. I sent it to them, they sent me back the same unit, repaired, and said they swapped the mainboard out in the repair notes. Worked great, except the device was completely wiped, relocked, unrooted, and they removed my nice Stenheil screen protector.
I was without it long enough that I got used to not having it. Since it was completly back to stock, I decided instead that I would sell it when I found a good buyer (friend, etc), and buy the new 2013 Nexus 7 instead. I found a friend who wanted it a few days ago.
I charged it over night last night so it was on a full charge this AM. I saw that I was still running 4.3 on it (hadn't really used it since I got it back in November), so I did the factory/official "OTA" update to 4.4.2 this AM. Went flawless, no issues, booted up fine. I updated all the apps on it, also worked fine.
I then decided to do a Factory Reset on it, (Thru Backup/Reset IN android, NOT
Recovery). I went thru the confirmations/warnings, and then it said "Shutting Down..." and, it shut down. I let it sit for a few minutes, expecting it to boot back up (it never did). I tried to turn it on, nothing. I tried ALL combinations of power + volume, + charging cable in/out, etc. Everything possible, trust me, I scoured the web for new combinations and timing ,etc. No matter what, I never got ANYTHING on the display, no charging indicator, no recovery or bootloader, nothing. It's like the display is dead. The battery was fully charged this AM after being charged overnight so I know the battery wasn't even close to low. It's like it's completely dead no matter what I do.
I then tried to hook it up to my PC, which is setup for ADB etc, couldn't see it in ADB. In Device Manager though, it's showing as being in APX mode? So I tried holding power down for 10 seconds with it connected, and it DOES disconnect from windows, and a few seconds later, it shows up again, again in APX mode. Nothing ever appears on the display. Holding VOL down or all three buttons while plugging into PC never changes anything, no matter what, it ALWAYS shows in APX mode.
From what I'm reading online, this is a sign that the bootloader is missing or corrupt, and, that there isn't a fix for that unless you first backed up your crypto "blob" using Flatline (which I didn't even know about till today). I'm hoping that maybe what I've read is out of date? Is there perhaps a way to fix or flash this yet?
The whole thing makes little sense. All I did is update it, then reset it, all officially supported/normal things, on a bone stock tablet. It seems more like they didn't ACTUALLY fix it the first time it went back to them....
Help? AFAIK the tablet is now out of warranty. I just want to sell it and get the 2013 model! The tablet is in perfect shape, it's been used with a screen protector and case since day 1 - not a single scratch on the screen or case.