Factory reset. Simultaneously press power, menu and volume up or down, the other position bringing up recovery.
I had unlocked the bootloader long ago, but had to re-root a couple if days ago in the process of updating baseband. I could update the rooted rom with LG's service flash tool w/o losing apps and settings, surprisingly, but could not get adb to work with Win8.1 x64. Trying to invoke fastboot menu on the phone earned me the factory reset, now all was gone and still no root and no way to recover anything. No problems with adb on the netbook running Win7 x64, however.