Is your Phone Froyo 2.2.2 .Did you install CWM v3.2.0.1 before you decided to reboot into recovery from ROM Manager. Do you have Busybox installed. Did you install the flash_image to /system/bin on phone.
There seems to be a problem with ROM Manager flashing the Recovery on 2.2.2 unless the proper flash_image is installed first. Who's method of rooting with the Gingerbreak.apk did you use.
It would be helpful to know the answer to these Questions so we can establish what you have actually done,and what more needs to be done,to help get you squared away.
Pull battery,hold power button down for 15-20 sec. Reinstall battery. Press home button+volume down,and then power button all at the same time. When you see the LG logo you can let go. If it reboots into a recovery with nine options and say's ClockworkMod Recovery v3.2.0.1 then your good. Volume up/down scrolls,camera button makes selection.
If you still get the black screen or only get to LG logo then give us the info requested above.