Buttons on touch panel of my DCR-HC21e Sony

This fault is often caused by a failing flat cable that connects the LCD panel and the rest of the camera. In its early stages it is possible to get the buttons on the touch panel to work by carefuly changing the angle of the LCD panel while trying out the buttons until you get a position where they work.
When the flat cable gets worse , the picture on the LCD panel will start deteriorating and go off altogether.
At this stage you may consider having the flat cable replaced.