@Praveen k: I'm not sure what could be causing this, and it is sadly difficult to troubleshoot the issue if you are unable to access the Settings of your device. Next time the phone reboots, don't unlock it, and instead press and hold the Volume Down and Power buttons together for around 10 seconds until the phone restarts. This will perform a Soft Reset and address any software issues that might be a contributing factor. Don't worry, this won't affect your personal data or settings. Further to this, you may also wish to check the Volume and Side buttons to make sure that they are not sticking, and forcing a restart in this manner.
If the problem persists then please head to samsung.com > Scroll to the bottom of the page > Contact us, and reach out via your preferred contact method, where an advisor will be able to arrange for the phone to be inspected and repaired by an authorised engineer.
