How about some more details on what happened and what you've already tried to fix the problem?
Maybe try the following:
1) Pull the battery from the phone.
2) Plug the phone into power. You should see just the physical buttons light up most likely. If you see the message to insert the battery already, proceed to step 4.
3) If you just have the lit buttons (but no screen message), keep unplugging and plugging the phone back in until the message to insert the battery comes up on the screen. Some people have said it takes a dozen attempts or more, but it's always done it for me after about 6 tries.
4) Once that message is on screen, insert the battery again. Your phone should show the LG Logo briefly, and then eventually go into the battery charging animation. If it doesn't get to that animation, then this isn't likely to work sadly.
5) With the animation onscreen, hold down the power button until the phone starts to boot again. Let it go once the LG Logo appears.
Also, since you've rooted your phone already have you rebooted into 'Recovery Mode'? (simultaneously pressing the 'Power' button, the 'Home' button, and the 'Volume-Down' button)