Windows 10 Update 3/16/2017 caused FN problem which installed Synaptics pointing Device driver version 19.0.9.5 (for Lenovo) conflicts with my Toshiba Satellite [L775-S7248].
I kept trying to uninstall, Windows kept reinstalling 19.0.9.5, even after deselect "Automatically get the device app and info provided by your device manufacturer." I tried Toshiba website for Synaptics pointing Device driver version 15.2.11.1, But Windows 7 driver will not work under Windows 10 and Toshiba does not support Window 10 for this model).
Solution:
Under This PC, under Manage, under Computer Management, under the Device Manager, under Synaptics pointing Device driver version 19.0.9.5 (for Lenovo), under Driver, Select "Roll Back Driver" It rolled itself back to 15.2.11.1 (2/3/2011). That stuck; Keys 1, 2, 3, and Space Bar are working. Device Manager no longer says Lenovo, but Synaptics PS/2 Port TouchPad.
Good Luck