If your laptop's touchpad isn't working when you try to use it, you may have accidently pressed the keyboard shortcut combination (Fn + a key), or the dedicated key which disables the touchpad. Also, if you have recently upgraded your laptop to Windows 10, it is possible that your touchpad is disabled. All you need to do in both cases is to enable it.
You can enable the touchpad using keyboard shortcuts (key combinations on the keyboard, e.g. Fn + a key), or via the operating system itself (Windows, MacOS).
Start -> Control Panel -> Mouse -> Click on the touchpad tab (Synaptic, Elan and etc.) -> Enable the touchpad
Start -> Settings -> Devices -> Mouse & Touchpad -> Scroll down to Related Settings and click Additional mouse options -> When the mouse properties window pops up, click on the ELAN (or SYNAPTIC) tab -> select your device and click Enable
Click the Apple logo at the top of the screen -> System Preferences -> Universal Access -> Select the Mouse & Trackpad tab -> Trackpad Options -> clear the Ignore Built-in Trackpad checkbox
Maybe a program you recently installed prevents your touchpad driver from functioning properly or is responsible for the touchpad scroll not working issue. Cleaning the registry should help you solve the problem.
The default touchpad settings may disable your device's touchpad when an external device (usually an USB mouse) is connected. You can change the default settings to avoid future conflicts.
To change the default settings:
Start -> Control Panel -> Mouse -> Select the Touchpad tab -> Search for options such as: USB mouse and touchpad behavior when USB mouse is connected
System Preferences -> Trackpad
From there you can also disable features like two or three finger scrolling, pinch zoom, circle zoom, rotate and swiping, if you don't need them. These new features may be the reason for the erratic cursor movement, since most are turned on by default.
Maybe an external USB device (e.g an USB mouse) automatically disabled the touchpad. Turn off the laptop, disconnect all external devices and then, turn it on again.
If the touchpad starts working, that means that one of the external devices prevented it from working properly; however, if your touchpad still doesn't work, then something else is the problem (check out the other solutions).
If you have bought a new laptop and you experience problems with the touchpad, take it back to the store and have it re-examined by the technical staff. They will diagnose the problem, repair the touchpad, or provide you with a replacement (if they fail to repair ir).
Run the Hardware and Devices troubleshooter (Windows)
Windows has a troubleshooter which can locate and fix the problem with your touchpad, instead of you. All you need to do is to run it.
To run the Hardware and Devices troubleshooter do the following, go to Start -> Control Panel (or type control panel in the start menu search box) -> type troubleshooting in the search box -> click on Troubleshooting -> Hardware and sound -> run the troubleshooters one by one.
Note: Do not interrupt the troubleshooting process.