When you installed adb, did you add it to PATH? If not, change to the directory adb is installed. Something like cd android-sdk/platform-tools. Yours may be different.
You can also try this. Uninstall the LG drivers. Reboot your computer. Install LG drivers again. Should be v3.10 I think. Reboot your computer. Also shut down your phone. And start it again.
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