Fixing up someone's laptop, mouse wasn't working... Fn-F6 isn't reenabling it... Try pressing just F6.
It activates the mouse
So there's a bunch of features bound to the function keys, like disabling the mouse or wireless (never liked that, helped out a few people who did that accidentally...) Normally you have to hold the Fn key while pressing F3 or whatever to access these extra functions.
Turns out that, by default on these Gateways, it's backwards. You have to hold Fn to access the real function keys... If you just hit F6 by itself, it helpfully disables the mouse. So crazy!
The original issue was that Cortana and the Start Menu were "not working". Which causes Windows 10 to helpfully offer to sign you out and try again. Explorer and everything still worked, just not their new silly phone-app nonsense...
All I did was reboot the computer a few times (trying to get to the recovery partition to restore it to windows 8 (it's new, the guy said a factory reset would be fine)). On the third boot Windows randomly started installing updates! It took a whole half hour, including another reboot, but when it finished it was working fine. Madness. The computer's had this issue for a couple of days, and hasn't had a network connection all day, yet it magically found these updates to fix itself. Magic.
Also I hate that computers these days have all sorts of different hotkeys to access the BIOS, and *no longer announce the button on bootup*. I'll hit delete, F2, F8, F12, F7, WHATEVER, just tell me. There's no reason not to tell me! (Searching for "Gateway BIOS Key" produced posts suggesting all those different keys. It was F2)