Default Xperia Z Tablet Won't reboot !!!

Hi,

I have just installed official ftf 4.3 update (from 4.2) via flashtool.
After complete, it is impossible to reboot it. Not even recognised as plugged on computer. Screen 100% off.

Does anyone have a solution for that as I have tried to get it charged and pressing power + vol+ (and vol- as well)
When pressing those buttons, only the led aside is blinking once white/red and then 3 times fast white, on loop...

Battery was at 60%.

Thanks for helping.