A few days ago, I came home to find that my laptop (a Dell Inspiron (?)) had powered off.
There hadn't been a power outage as far as I know. When I booted it up again, the mouse
pointer no longer responded to the touchpad, either by motion or clicking.

I've found a number of webpages and videos talking about how to fix a recalcitrant
touchpad on Ubuntu, and tried many different fixes. Diagnostics such as

xinput list

and

less /proc/bus/input/devices

and

xsetpointer -l

suggest that the problem is in software rather than hardware. The Synaptics
touchpad is recognized and listed in all those programs' output.

However, none of the software fixes I've tried so far have worked:

- gsettings set org.gnome.settings-daemon.plugins.cursor active false

- installing xserver-xorg-input-synaptics

- installing ubuntu-restricted-extras

- editing /etc/default/grub to add "i8042.reset" to GRUB_CMDLINE_LINUX_DEFAULT
(and running update-grub afterward)

- adding psmouse.proto=bare to GRUB_CMDLINE_LINUX_DEFAULT
(did update-grub and rebooted both with and without the i8042.reset parameter)

- installing touchpad-indicator

- do Ctrl-Alt-F7, then Ctrl-Alt-F1

- do Ctrl-Alt-F5, then Ctrl-Alt-F1

- `modprobe -r psmouse` followed by `modprobe psmouse proto=bare`

Not necessarily in that order. I rebooted after most of those fixes, either immediately or after trying another fix. The mouse pointer still doesn't respond to the touchpad in any way. Any
more ideas?