My phone is rebooting on its own My phone ( Xperia Z ) is restarting on its own every second its not coming up to the homescreen when its restarting it hangsup and restarts again i have no option of connecting it to my pc as well, as it doesnt get detected. i want to reinstall OS in it is there a way, can someone help me on this..??

It doesnt matter if i have to root my phone or pay and get a OS i want my phone to work ??
In my case, I did a factory reset. 

To do this: Open your phone in recovery phone. Hold down the home button, the volume down button and simultaneously press the power button. Your recovery mode menu should have an option about factory reset. Unfortunately, you will lose your apps and maybe your contacts/sms(unless you have back them up).