Do you mean that your phone is dead? In that case I suggest that you charge your phone for a couple of hours. Remove the battery for a while and then try to start it.
If the phone still doesn't start I suggest that you repair the phone software using PC Companion:
http://www.sonymobile.com/update
In PC Companion, press start on Support Zone > Start on Update the phones software > Press the blue link that says "Repair phone". Do this without the phone connected to the PC. Then follow the instruction given to you in the program.
