Did you per chance just upgrade to Window 10 right before it happened? If that is the case, this happens a lot.
Try the following and see if it fixes it...
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".
It should work now.
Also, you might also want to check for updates to your drivers.