Flashing Original Firmwares

This can take a while, so bare with me. There are few steps to follow.

Step 1: Downloading Original Firmware

Open LG Optimus One Firmware List

The download link is

http://csmg.lgmobile.com:9002/swdata/WEBSW/LGP500/XXXXX/V10a_00/V10A_00.kdz

where XXXX is code from link above. For example:

I want to original LG firmware for czech republic.
1) Open LG Optimus One Firmware List
2) In browser I will start search czech/cze and it finds something like

Code:

CDMA LGP500 ACZEBK CZE/CZECHO - Unbranded FW CDMA LGP500 ATMCBK TMC/T-MOBILE(CZECHO) - Branded T-Mobile fw CDMA LGP500 AVDZBK VDZ/VODAFONE(CZECH) - branded Vodafone fw

where ACZEBK or ATMCBK or AVDZBK are code for download link.
3) Go to

Code:

http://csmg.lgmobile.com:9002/swdata/WEBSW/LGP500/ACZEBK/V10a_00/V10A_00.kdz

for download unbranded LG firmware for czech
It's not confirmed, but you can also try V10x for new version of firmware. Maybe it will work, maybe not.
IMPORTANT NOTE!!!
For different version you have to change also path in url!! ex:

Code:

For V10a_00 http://csmg.lgmobile.com:9002/swdata/WEBSW/LGP500/ACZEBK/V10a_00/V10A_00.kdz or for V10f_00 http://csmg.lgmobile.com:9002/swdata/WEBSW/LGP500/ACZEBK/V10f_00/V10F_00.kdz

Next:

1. Download KDZ updater and uncompress it
   
2. Install msxml.msi from the uncompressed directory
3. Conect your device (do not turn on disk storage) and run KDZ_FW_UPD.exe (Has administrator).
4. Select Type : 3GQCT
5. Select PhoneMode : DIAG
6. In KDZ file : Choose the ROM file you downloaded in the first step
7. Press Launch software update and wait (It will be 10 minutes or so). In your phone it will appear "Emergency mode". Wait until it reboots.

And you're done!

Original content from xda-developers.com