Hi @siew, sorry to hear about this. 
Does the restart occur when you are doing anything specific in the device, such as using an application, or a service?
A good place to start is to remove both the SIM card and SD card from the device. If any of them are defect, this can cause the device to restart.
Should there be no change, try restarting the device in safe mode, so we can see if any of your downloaded applications are the cause of this, as they are temporarily disabled in this mode.
Let me know how it goes!
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