Originally Posted by ShadySquirrel
If I remember correctly (please check threads here, it's been a long time since I've used this device, so memories are fading), download mode is activated when you press Volume Up (or both of volume buttons) and insert USB cable. I know that E98x has some strange button sequences, like rebooting to recovery is a two step operation (Volume Up + Power until navbar blinks, then power button twice, that's the only way mine wanted to boot into recovery), so please check around.
As far as USB connection issues, don't use USB3+ ports and if you're on Windows 8.1+ and later, run with Administrator privileges. I never experienced that one (used LGFlashTools from inside VirtualBox running Win XP for all my needs, I'm not a Windows user), so can't really help much but forums are full with explanations how.
Thank you very much...now the phone is back to initial state. This what i've done:
1. Download LG Flash tool from http://lgflashtool.com/
2. Download LG USB Drivers from http://lgflashtool.com/
3. Install LG flash tool and LG USB Drivers
4. Plug usb cable to phone
5. Hold volume buttons and then plug the usb cable to PC (i use win 10)
6. Voila, the Download Mode icon is showed up
7. Run LG Flash Tool (Administrator privilege) & follow the instruction (i use e988 v20c stock firmware)
8. Phone back to normal (only if you use the correct stock firmware)
A very big thanks to ShadySquirrel
Hopefully this thread can also be used as reference for anyone who has the same issue as i had