So here I want to show you how you can restore completely died LG p760(or his brothers p765/p768/p769) showing nothing or just LG Logo and so well known "Security Error", or boot loop problems.
The goal is to flash stock recovery, x-loader and u-boot and to unlock the bootloader(u-boot), so it can boot Clockworkmod or TWRP recovery.
First of all you'll need a computer(preferably Win7/8), an died phone , some drivers on the computer and fastboot on the phone. Let's start.
I'm not responsible for any damage to your device made during this guide. You can continue at YOUR OWN RISK.
Please READ IT before taking any actions on your phone!
1. Get fastboot on the phone. How? You can see here and here, or search the internet. There is a driver package, install them following the instructions.
2. After you inserted phone, installed drivers, etc. start the fastboot loader script(I prefer Lelus's one, i'ts more option-rich), and select one option for ICS x-loader and u-boot for your phone. Follow the instructions, it may take 2 or 3 tries before the drivers are correctly installed. Start again if the drivers are not correctly installed.
3. Copy the bin folder that is inside the fastboot files folder in C:, press winkey+R, type cmd and press OK.
Then copy everything from v20c_00 folder inside the C:\bin\ folder, it's in attachments in the end.
Here is the time to say that this files are for p760 only, you can find x-loader, u-boot and stock recovery for you model from internet, or here in the forums. I flashed also the boot.img, but don't think it's necessary for the completion of the process. You can also extract the .img files from stock .KDZ rom with this tool here, thanks to user kuma82. In the archive is the tutorial how to make x-loader.img, it's easy.
Then after you copied the files from archive, or files that you extracted from your stock rom, type in, or copy and paste into the cmd window:
fastboot erase x-loader fastboot erase u-boot fastboot erase boot fastboot erase recovery fastboot flash x-loader 0-x-loader.img fastboot flash u-boot 1-u-boot.img fastboot flash boot 2-boot.img fastboot flash recovery 3-recovery.img
After all the commands are completed without any errors, plug out usb, plug out battery, put the battery in, start the phone. The "Security Error" message MUST be gone. If it's not, probably your recovery is wrong, flash recovery again, if not, try with other recovery. This is working on P760, at least on mine. Here the S/W Update mode must also work like a charm, and you can try with some KDZ updaters, but that's not for this tutorial.
4. Now for step 4 we will need the phone in Recovery Mode. With phone turned off and battery inserted, press VOL_UP+HOME+POWER, when LG logo shows, release POWER and hold other two while the LG Recovery Mode show up. The phone must go straight into recovery, not bootlooping or showing "Security Error". If this happens, probably you recovery or u-boot is wrong.
Now put the usb into the phone and install the drivers from usb_drv_windows folder that is in the fastboot archive.
5. Type into cmd window:
Then we will unlock the bootloader with this command:
6. The phone will go into fastboot mode itself, you must install the drivers, again from the folder in the archive.
Now we'll flash CWM recovery with the help of fastboot. Copy the recovery-clockwork-18.104.22.168-p760 or recovery that is for your model to C:\bin\ folder.
fastboot flash recovery recovery-clockwork-22.214.171.124-p760.img fastboot reboot
7. If everything is successfull you phone will load the recovery and you will be able to load nandroid backup or stock update.zip or CyanogenMod on your phone. Don't forget to wipe cache/data and dalvik's cache. From here you can backup your data or do whatever you want.
If your phone is not totally bricked, and if you are lucky enough you can continue from step 4(if you have recovery in your phone and it's still loading).
I want to attach them here to the forum, but I can't for now, so here is Google Drive folder.