Some things to try if your touchscreen doesn't work...
1. Restart the computer. Sometimes that is all that it needs.
2. Go to "Start" and in the search box type "Calibrate the screen for pen or touch input". Choose the top result. In this new screen click "Setup" and follow the instructions.
3. Go to "Control Panel" and then "Device Manager". Select the "Monitors" section and right click on your monitor. Check the information for the touch screen and make sure it is "enabled".