touch screen fault?

Recently I turned my Nuvi on and was asked to press a dot on the screen to update programmes. The dot changed position several times asking to be pressed again. After a series of presses the normal screen appeared and all seemed normal except .... the touch screen has gone wonky. I have to touch above or below each character to correctly select the item wanted but, worse, I can only get as far as the screen when I need to press the green 'DONE' panel in the bottom right hand corner but this will not respond. Any ideas will be gratefully received. Chris M.