Unfortunately even using a USB 2.0 port did not work. I don't have much hope for it since I was able to connect over fastboot and EDL previously but it currently won't connect over USB at all.
I even tried putting it in the freezer in case the issue was something similar to what happened with the good old Note 4, but that only made it draw ~140 mA while it was cold instead of ~450 mA, still no indication of connecting on either of my computers.
What I can see/access right now is:
1. "V40 ThinQ Powered by Android" boot screen, then goes immediately to red triangle (specifically this time there is no "all slots are unbootable" message), then to V35 fastboot:
View attachment 5336015View attachment 5336017
2. EDL mode (I think). I hold power + volume down while in fastboot and then rapidly push the volume up button. If timed right it goes to a blank screen instead of rebooting to option 1 (V40 boot screen etc.).
3. A circle with a lightning bolt (presumably the charging screen) shows up momentarily -> red triangle -> V35 fastboot.
4. Factory reset screen (tried resetting, it didn't change anything)
View attachment 5336021
Maybe there's some magic key combination or something to be discovered in the future involving a microSD card (if it's even a software problem, perhaps some chip or fuse blew and that's why it won't connect over USB) but I think my V40 is now a fancy paperweight/parts phone. At least it was less than $100!
Obviously the phones not dead, it's just not booting. It's possible the usb port has gone bad, some say using a q-tip and isopropyl alcohol to clean it helps.
Be sure, in device manager, that you don't have anything with a '!' symbol (like android, etc), as that would mean a driver problem. I know you said it was working before, but check that again as windows can be very finicky.
Does the pc see the device using lgup? (device off, hold vol up, plug in usb cable). Yeah the usb problem needs to be figured out first. Seems possible, given the price u paid, it might have been bad to begin with and only worked intermittently?