Plugging the phone into USB 2.0 makes the phone show up in portable
devices, but LG Suite fails to identify the phone. I tried using both
LGE Android Net MTP USB Device and MTP USB Device but they both fail. I
have LG United Drivers and LG Suite installed already.
You must be on 64 bit windows. Not even on 64bit, Still try this...
1) Uninstall LG Drivers, LG PC Suite and anything you see named LG. Restart PC.
2) Install latest LG Driver
from this post (step 4)
3) Install Optional MTP Driver
from this post (step 4)
4) Open Windows Device Manager (just to watch whats happening.)
5) Disconnect Internet (To avoid stupid online WDM drivers)
6) Connect phone with Usb and let drivers install automatically. Give it
some time to install drivers keeping watch on Device Manager window.

7) Keep changing USB connect modes to all modes one-by-one on Phone and let drivers install.
You should see MTP drivers installed now. If this does not help, cant
think of anything else. If this works, press THANKS button
EDIT: Connect USB at backside of pc, directly to USB on pc motherboard.