If you reboot and your touchpad works again, you've found your issue. Depending on your computer, you might be able to tweak this setting to keep your trackpad active even with a mouse plugged in (see below for more on this).
If you reboot and your touchpad works again, you've found your issue. Depending on your computer, you might be able to tweak this setting to keep your trackpad active even with a mouse plugged in (see below for more on this).