Well if its stuck on the intro screen, take out the memory card if you have one. Otherwise I'm not sure.
Why Won't My Lg Rumor Turn On?
You can try either charging it or unplugging it, if that doesnt work then you have to go to the sprint store and get your phone traded in. Hope that helps!
Try turning it off for 60 seconds, if that doesnt work, remove the battery and remove the sim card, and then put them back in and try turning it on, if that doesnt work, it could be damaged and you should bring it in to be looked at