My Lumia 720 is asking to switch to power off again and again, why?

[Windows Central Question]

My lumia 720 is asking to switch to power off again and again

my phone lumia 720 is automatically switch off and auto switch on. i visit Nokia care they told me belt is not working and replace it but the problem is as it is..when i just normal touch a lock button then screen down and ask me for switch off this slid down again and again when i slid down screen they switch off and start automatically...