Inspiron 15 N5010: Keyboard works in BIOS and will not work at OS init

Got a super strange issue here on an Inspiron 15 N5010: When the system starts up F12 and all other keyboard input works just fine at the BIOS level. As soon as the BIOS bootstraps over into the OS booter (Windows 7 and 10 via a USB boot flash drive), all keyboard input ceases.

An external keyboard behaves identically. 

Fn + function keys DO still work at this point (ie, the screen brightness will decrease/increase whilst repeatedly pressing fn-f4/f45).

This has lead me to believe that the keyboard in and of itself is fine and that this is a problem with the laptop BIOS or system board...  Any thoughts? 

I'm not seeing a clear way to update the BIOS since I can't even boot into Windows at this point and get any kind of input. The system hangs on the black screen just prior to booting Windows and gives the option to delete restoration data, but since I can't click it, it just stops at this screen. On Windows 10 boot, it simply hangs prior to booting the OS.