Windows 10 Update 3/16/2017 caused FN problem and installed Synaptics pointing Device driver version 19.0.9.5 (for Lenovo) conflicts with my Toshiba Satellite [L775-S7248].
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 worked; Keys 1, 2, 3, and Space Bar are working. Device Manager no longer says Lenovo, but Synaptics PS/2 Port TouchPad.
Good Luck
Notes: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" (above). I went to Toshiba website downloaded, but would not install Synaptics pointing Device driver version 15.2.11.1, (Toshiba Windows 7 64 bit would not not install under Windows 10, I could not find one under Windows 8, and Toshiba does not have any support for Window 10 for this model on their website).