Optimus G E975 won't start with red flashing led topic

Hi all, I managed to brick my Optimus G E975 (international version) - the inside of the phone shows E975K.

I have it running the stock ROM for over a year (rooted) and lately I am looking into flashing with custom ROM (KitKat). I have not even flash the phone, I just installed ROM Manager app (pro) and used it to boot to recovery. It won't boot to recover, so I use ROM Manager app to install TWRP (to replace clockmodwork). I booted to recovery and I got the fastboot but could not do anything so I rebooted to normal and install clockmodwork again. There was an option to Flash clockmodwork which I think I chose and I assumed that was installing clockmodwork. But when I booted to recovery, my phone never turned on anymore.

While I got my phone working, using ROM Manager I tried few times to make a back up of the current ROM but it was never succeeded. The phone just rebooted normally.

I opened my phone and disconnect the battery as some people suggested. But I still can't turn on the phone. I got flashing red led when I press the power button (with or without the vol up/down).

Please help. I hope I can unbrick my phone as the warranty is over.

Any info and help would be appreciated. Thank you.