Whenever I use my external mouse with my laptop, I physically disable the touchpad by pressing a button. Ubuntu detects this switch correctly, and will display an overlay that shows the current state of the touchpad (enabled or disabled).
However, I do not enable it again before shutting down the system. When I reboot, the touchpad is physically enabled by default, but Ubuntu remembers it as disabled.
Ubuntu loads with the system thinking "touchpad disabled", so I cannot move the pointer. When I physically disable it, the system thinks it's enabled, but of course I cannot do anything with it either.
Is there a way to make the system forget the touchpad state on shutdown and then have it detect that properly on boot? I think this is strange and even idiotic behaviour, the system should not rely on some file on the hard disk to detect whether the touchpad is enabled. Persisting such state by default is useless in my opinion.
There are other people that had similar problems, but they used software. I use only the default system settings. I know that it is possible to make the state of the touchpad depend on the external mouse being plugged in or not, but my external mouse has a very small connector that is designed to stay plugged in at all times. Very handy as it doesn't get lost and I don't have to pull it out and push it in all the time.