Have you tried rebooting the computer? Sometimes that is all you need to do.
If that doesn't resolve it, try the following and see if it fixes it... you may need an external mouse to make the changes until you get the touchpad working again.
1. Go into "Control Panel".
2. Click "Hardware and Sound".
3. Now click "Mouse and Touchpad".
4. Now go to "Additional mouse options".
5. The Mouse Properties window will open. In here click on your device.
6. Make sure your device is set to enabled. If it isn't then click "Enable Device".
7. Exit both that screen and "Control Panel".
Also, you might want to check for updates to your drivers, including the Synaptics drivers.
If this does not help, and an external mouse works fine, then it may...