If your touchscreen is not working:
Make sure you have removed the plastic screen cover that comes with new devices;
Try restarting the device
Hold down the power button, wait for it to turn off, wait 3 seconds, turn it back on
Try cleaning the screen
Using a soft lint-free cloth
If both of the above don't work - perform a hard reset:
Hard reset
Turn the device off
Remove the battery from the back of the device
Wait 3 seconds
Reinsert the battery and turn the device back on