If you're black screened due to having a recovery installed that does not have the appropriate drivers for you s-screen phone, then look here:
[FIX]Black screen with custom recovery and custom roms - Android Forums at AndroidCentral.com
Sounds like you've done a factory reset on your rooted phone which is discussed here:
http://androidforums.com/optimus-v-...4-do-not-factory-reset-your-rooted-phone.html
Keep in mind the factory reset discussion was initiated prior to new s-screen phones being scattered across the market. If you're running 2.2.2 by default you likely have one of the s-screens. The older version shipped with 2.2.1 on it and wasn't afflicted with the dreaded black screen as the appropriate drivers were baked into the ROMs and recoveries.
There are ROMs and recoveries that work for either version here:
https://github.com/inferiorhumanorgans/android_device_lge_thunderc/wiki/Binary Just need to choose the appropriate one for your setup.
Personally I've used the BobZhome recovery (
VM670NH_recovery.img) on my 2.2.2 versioned s-screen OptV without any issues. I can't vouch for other recoveries as I haven't tried them, but I'm sure there are others out there who can share their experience.
Otherwise read, read, read and ask lots of questions. Lots of good resources on these forums!!