Maybe the battery has died. Try charging the phone and see if it helps.

The battery is fine, you have more then likley cracked the motherboard, or its software related. Either way have it repaired under warranty or go to a phone repair store.

My wife had an LG phone she really liked but then wanted a RZR so we changed over when it was time to upgrade. She used her phone for a while and then started having problems so AT&T sent another to replace it. She went back to her LG phone and then it eventually died so she started using a phone her sister gave us which were functional, they had just upgraded their phones and had them left over. We after starting to use another Motorola phone, it started acting up so we decided replaced the SIM card with another one we had and registered it with the phone through AT&T. It worked for a while and it started shutting itself off and I then bought her another of the LG phones she really liked and now it has started to shut itself off. I called AT&T several times and then finally went into a store and got a brand new SIM card and it started doing the same thing. I then though maybe that it wasn't getting a good charge in the outlet her charger was plugged into so I can an extension cord out of our bedroom into another room on a different circuit but it stated shutting off again. She is now stuck with a brand new phone that I purchased which is having the same problems her previous three phones have had. A weird thing is that we have 5 phones on our line and no one else had experienced this problem until the other day when my phone had shut itself off two days in a row, RAZR model. I am really getting so mad about these undependable phones, we are thinking of buying the new iPhones when they come out in July hoping they are better. Had anyone else had this much trouble with cells? I as a guy at Radio Shack if he had ever heard of problems like this and he said it has something to do with AT&T switching their equipment and the phones are out of synch but I wonder if that is the case, how do you get them in sync?