This may be a battery problem. Did you leave your phone charging all night? If you did this, is probable that your battery went bad. Open your phone and remove the battery to check if your battery seems to have swollen, if it did you will need to replace it. If you don't notice any swelling then connect your phone to the charger and check if the charging light turns on, if it does but the phone does not seem to charge then you will also need to replace the battery. Finally if the battery seems okay then you may have a problem with your turn on button, one possible cause is that there is something obstructing the key to be successfully pressed. To fix this you will need to open your phone, then clean and push the keys from the inside of the phone. Please go to this troubleshooting page for more information on your problem: [[Sony Xperia J Troubleshooting|Troubleshooting]]