Touch screen issue with SONY XPeria Z2 tablet

Hello All,
I have bought a SONY XPeria Z2 tablet. It is all working fine, but the screen touch seems to have some issue.
It is not recognizing the touch. Sometimes when I open all applications everything except the bottom android buttons become non-responsive. Sometimes the lock screen not recognizing the touch.
Is this a problem with the settings or hardware issue itself? How can I troubleshoot this issue? Any kind of help will be very much appreciated. Thanks a lot in advance, guys!
