[Nexus 7 Q&A, Help & Troubleshooting] BrightHeart:
I was running stock rooted Android KK 4.4.4 on Nexus 2012 Wifi Only with bootloader as unlocked. I attempted the Lollypop update 5.0.2 by OTA but it gave an error while installing and device rebooted to Kit Kat normally.....working fine. OTA was not getting done for some reason may be because i was rooted.

I downloaded the factory image nakasi-lrx22g-factory-2291c36b.tgz from google and attempted to flash it using Nexus Root Toolkit(v 2.0.2) with option "No Wipe Mode" as selected and then the device ran into fastboot mode... NRT run commands like erase system etc then the script gave an error "Failed" "remote -invalid state" while attempting to write bootloader. I thought that the problem is with "No Wipe" selected so i re-attempted it with "No Wipe" being unselected. BUt same error.

I searched the forum & found that the issue may be due to incorrect/corrupted bootloader. I replaced the bootloader-grouper-4.23.img which was in the factory image with the 4.23 bootloader taken from JWR66V as most people over XDA have said that its the working bootloader.

I had flashed the img downloaded from here - http://xdaforums.com/showpost.php?p=45043044&postcount=15

Flashing succeeded and Nexus Root Toolkit did not give error this time it said "OKAY" instead of "FAILED". But it did not proceed forward to flashing other files like system img etc. NRT was stuck at the Flash Bootloader - OKAY cmd.

I powered of the Tablet and Powered On again it showed "Booting Failed" at the Google Screen. I rebooted into Fastboot mode with "vol- and power" held together. It displayed the same screen as it did before i.e. displaying the information of Bootloader.

Product Name - Grouper

Variant - Not Defined Yet

HW Version - ER3

Bootloader version - 4.23

Baseband version - NA

Signing - Not Defined Yet

LOCK STATE = UNLOCKED

Then I read somewhere that after flashing the Bootloader img you have to run the bootloader by rebooting tablet with vol+,vol- and power button all held together.

I did that and wat i saw on computer screen was "APX device found" :((((((

The device went into APX mode and since 2 days has not come out.

I tried pressing Power button for like 3mins with power adapter connected/disconnected by usb

I tried pressing vol- and power button for more than 5min. with system connected/disconnected with usb

Nothing worked...

I am wondering what took the device to APX because the bootloader was good one from "JWR66V". It was flashed with success by Nexus Root Toolkit. the device did run into fastboot mode once after flashing it. The Device went into APX after all the 3 keys "vol+ vol- and power" were pressed together. But according to key combo terms APX mode is activated when "Power" and "vol+" are pressed and it exits when "Power" alone is held for 15+ seconds.

What I feel now is that the device is in APX looping (similar to Bootlooping) due to some reason. Corrupted Bootloader can be one of that but its unlikely as flashing was successful and img used was authentic. One more reason of APX looping may be that nothing apart from Bootloader is present in it, no system no recovery. only bootloader is present.

Now what do I do to come out of APX ? Power button and Power+vol- etc not working tried them numerous times. It won't accept fastboot or adb commands as its in apx mode.

Its Out of Warranty so only 2 options left for me now

1. Battery Removal

2. NVFlash

I want to keep things simple so I am thinking of battery removal first. Does the battery removal reset nexus 7 ?

I have a feeling that its effect is same as the power button holding for 15sec. but will have to try. Although the Warranty is voided but will Asus people agree to provide paid service to me if i myself attempt battery removal by opening the back side of the device.

Incase this dont work I will move to nvflash

But I have a few questions regarding nvflash.

1. Does nvflash require blob n sbk even for an unlocked bootloader?

2. I can generate the SBK for my device using the CCSN number and try though but I want only a simple command which will reboot nexus into fastboot mode exiting APX mode.

any help will be appreciated.