Help! My XZU is dead

You haven't unlocked your bootloader.

The flashing Red LED is the notification that a locked bootloader has encountered a ROM that is not based on Sony's releases. (CM, AOSPA, AOKP and so on.)

You need to unlock your bootloader to flash any ROM found in the Original Android Development section, and in the other Dev section only those marked LB can be installed with a locked bootloader.

http://unlockbootloader.sonymobile.com/instructions

NOTE: Doing so will erase the TA partition (which holds the DRM keys which allow X-Reality, Gracenote and other things to work.) and WILL NOT BE RECOVERABLE unless you back it up.

To back up the TA partition you will need to be rooted on a stock ROM.

Read the following thread, then read it again three more times before proceeding any further.

http://xdaforums.com/showthread.php?t=2569904

And if you bought your Phone from Bell Canada, they won't let you unlock your bootloader.

sarkis.tufenkji said:

My phone is rooted and my bootloader is unlocked, I was running AOSP ROM, after returning to stock rom it didn't boot. When I connect my phone to the PC the red led lights up and after 3 seconds it goes off, it keeps connecting and disconnecting

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How did you return to stock rom?
What rom or FTF did you use?
How did you flash it? Flashtool etc? what version of the program did you use?
How much charge was on the phone when you did this?

sarkis.tufenkji said:

I used flash tools to flash stock rom with flashmod and its the latest version of flash tool
I used C6802_14.2.A.0.290_Generic ME.FTF
my phone had almost 70% charge on it

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what version of flashtool did you use?? cause there is a bug with a previous flashtool software version. the bug is that it bricks your phone...

hamdogg said:

what version of flashtool did you use?? cause there is a bug with a previous flashtool software version. the bug is that it bricks your phone...

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Click to collapse

I also think the last brick used that C6802_14.2.A.0.290_Generic ME.FTF firmware but I cant find the thread