Just wanted to leave my 2 cents here, I've been trying to do my best since around august 2014, no success. 2 days ago I retried this, and I DID IT! I will tell everyone what I did very shortly:
My problem that I solved: I can boot, device works like a charm. But: no boot logos, no recovery.
My solution for TL;DR: UNINSTALL ALL DRIVERS FROM DEVICE MANAGER 1ST, then reinstall. After that, flash a fastboot ROM and use it to WIPE ALL THE DATA IN YOUR PHONE! THIS was what I needed and was never explained: you had to WIPE the old data in order to get the boot screens back.
IN THIS ORDER (THANK YOU to those people from previous replies, gathering all your info was of great value):
Uninstall all of your phone drivers from your PC!!! This is what made most of my headaches go away, just use Device Manager and uninstall anything from LGE. After that, plug in your device in your USB ports (always BACK ports, not front ports, important). It should detect all drivers and download them.
IF it fails (it generally does with LGE USB Modem), you can go to Device Manager > Unknown Device (the one that wasn't recognized) > Right Click and Update > Choose 2nd option, then choose "choose from a list of local controllers" (or whatever the button says). After that, scroll down to LG Electronics, Inc. and install what didn't install.
I also found these drivers, but I did not test them: http://www.mediafire.com/download/p6...r_LG_GT540.zip
Now you're set to begin:
FIRST thing you wanna do is a factory reset, this is something I'd forgotten with time, don't make the same mistake as I did. You can do it by turning your phone on and pressing Volume +/- & Home & Quick Search buttons all together for 5 seconds (it works, be patient and wait for it, even if you open the camera or any other stuff).
Download this Google SDK Tools
(unzip and put the folder in C:\ drive) and this Fastboot drivers for GT540
(unzip and put the files inside the folder in C:\android-sdk).
Skip this next line if you know your ROM has fastboot.
Since you have Fastboot enabled, now all you need to do is turn off your device (all this with its battery on it, no weird things) and hold the Camera button before turning it back on. This should take you either to a black screen, or simply to no display, like me. Either one will work anyways.
Now press the Windows key > Type cmd and open it with Right Click > Run as Administrator.
In it, type all this, command by command (you can paste by right clicking):
fastboot erase boot
fastboot erase system
And now it's go time! Do what everyone else says in here: Take out your phone's battery, SD and SIM cards, fire KDZ Updater up as Administrator (If your KDZ freezes, then it's either faulty or you did not install msxml, look for a good KDZ that comes with that file and delete your current one), choose CS_Emergency PhoneMode and:
1-Plug your phone while holding the volume DOWN button (don't worry! My phone didn't show "Download Mode" either, if you hear the Windows "Somethingpluggedin" Bump noise, it's ok).
2-Flash French V20A
3-Unplug your phone once KDZ says "==FINISHED==".
4-Plug it once again, holding the volume DOWN button.
5-Flash out.kdz (remember! it's CS_Emergency).
THANK YOU XDA!