Turns on, then shuts off right after

My sister has an LG Rumor LX260 That she has had for about 6 months, and recently, she gave it to me, and told me that one morning, it wouldn't turn on and that she wanted me to try and wix it to save her contacts for work, friends, etc. When i tried to turn it on, it showed the boot screen for about 7 seconds, and shuts off. after trying to get it to work, was to boot it without the battery, and when it booted up to the "Battery Required" screen, and when i put the battery in, it showed the charging screen, and underneith it, "power off" so when the end button is pressed, it will shut down. I can't seem to get it any further than that, and when disconnected while the charging screen is showing, and it is unplugged, it shutts right off. I ordered a battery, and that didn't solve the problem, and can't find any repair manuals anywhere to take it apart. Anyone have any ideas?