Symptoms: your touchpad works on the login screen, however once you've logged it, you can't move the mouse cursor. I experienced it under openSuse, however it may alos come up under other Linux versions using Gnome.
The problem: the maximum/minimum speed got reset to 0.
The solution (this is openSuse specific):
- Start the control center (Ctrl+F2 -> gnome-control-center). You should be focused in the search box
- Type in "Touchpad" (probably a prefix of it like Touch will also do). Tab your way to the "Touchpad" icon (I needed to press "Tab" 4 times) and press Enter
- Now you should see the "Touchpad Preferences" window. You can navigate it using the following keys:
- Tab to navigate between the controls
- Ctrl+PageUp / Ctrl+PageDown to navigate between the pages
- Space to check/uncheck options
- Left / Right arrow keys to change sliders
- Make sure that none of the sliders are all the way to the left. Also make sure that the "Enable Touchpad" option is checked. The effect is instantaneous, you don't need to click any Ok / Apply button (Gnome style).
Hope this helps.