after i install 4.3 version and reboot the system my phone does not turn off any more just display htc one ...if u hold the power button still it return to htc one only..please help.
If I remember correctly, you can do a hard reboot on the phone by holding down the power button for about 60 seconds. If I remember, that is the way to stimulate a 'battery pull'.
I actually have the HTC One myself, but I only had to do a hard reboot once myself.
If that does not work, then I would recommend doing a Factory Reset.