Install driver LG P500, you can find it at LG official homepage or download below
After install the driver restart you PC/Laptop then go to Control Panel -> System -> Hardware -> Device Manager -> Modems -> Right click LGE Virtual Modem, choose Disable.
KDZ Updater, we`ll need it for flashing firmware. download and extract kdzupdater and install the msxml.msi
LG Optimus One Firmware that suitable with your region (in this tutorial, using firmware v10c singapore region)
Note: It`s better idea to close similiar application, such as KIES, ovi suite, BB desktop manager
How to Flashing LG Optimus One back to Original Firmware
Turn off your cellphone
Press and hold Volume[+] + Power + Back buttons, until your Optimus boot in emergency mode
Connect LG Optimus One to PC (via USB) tips: maybe it`s a little strange to do, but you can try to shake the phone if it can`t detect.
Select Type : 3GQCT
Select PhoneMode : DIAG
tips: if this option failed try EMERGENCY or CS_EMERGENCY
At KDZ Files section, select firmware that you already download
Click launch software update button tips: someone say that it`s good idea to shake your optimus one with gently to avoid stuck.
Wait until it`s done, unplug the usb cable
Press and hold Volume[-] + HOME + Power buttons
See the firmware version, congratulation you did it