Found a way how to fix my problem. This should work for almost all bricked phones.
Remember, this will wipe ALL DATA from your phone. I'm not responsible if something happens with your P970. Do at your own risk.
You will need:
Drivers for P970;
Start from here if it's first time (no drivers installed, etc):
1) Install all drivers (from Drivers folder);
2) Disable LGE Virtual Modem (Control Panel > System > Hardware > Device Manager);
Start from here if drivers already installed:
3) Run msxml.msi (in KDZ_FW_UPD folder);
4) Delete mfc42.dll (from KDZ_FW_UPD folder);
5) Run WindowsEnabler.exe and set it to ON;
6) Run UpTestEX_mod2_marwin.exe;
7) Set your phone to S/W Upgrade mode (take out battery, while pressing Volume Up, plug USB cable).
1) Select KDZ file (download from here);
2) Click "CSE web upgrade test", then "Upgrade Start".
Chose your language and wait till phone reboots. It will take some time and could look like nothing is going on. If you see something similar to this (on your phone) for a moment, everything went OK.