Touch screen not operating correctly

My sons' DS lite (a year old) was dropped and although no obvious damage, the touch screen is not working properly. Although the touch screen responds to most taps with the stylus, it appears that the positioning is not right and 'off position'.

I have tried caibrating, and although I can tap the stylus on the small red boxes during this process, the calibrating procedure does not 'finish' and check positioning via red squares that turn blue in the final check. Instead, the program keeps looping around the calibration sequence, asking for stylus input for LH top red square, bottom RH and and middle - taking all of this in and going round again and again in this sequence. Is this a programe/software fault or something broken within the screen??? What should I do??