First, no matter how you fix it, remove ROM Manager once you are booted back up.
Can you boot into recovery? In case you don't know how: power off, then hold home_key+down_volume+power till the LG logo disappears.
If yes: Read the stickies and pay attention to how to setup ADB.
Use ADB to push a proper recovery for the Optimus V,
Then use ADB to remount system,
Then use ADB shell to flash a new recovery.
Reboot into the new recovery, and flash the ROM zip file.
--If it still doesn't work, the ROM zip file got corrupted during file transfer, re-download, ADB push to sdcard, and flash it with recovery.
If no, you cannot boot into recovery: Once you see the bootanimation begin, you should be able to use ADB and follow the same steps mentioned above, but you may need to be quick about it, since the phone could be freezing during boot up. If it does, try to push during one boot-up, pull the battery, then ADB shell flash_image during the next boot-up.