[HighAltitude]

After flying uneventfully for more than a year (including 3 flight modes), my S450 quad suffered a "mishap" necessitating replacement of the lower frame/PD board.  Replacement was a simple matter of unbolting the damaged board,  desoldering/resoldering the ESC power wires, and bolting the new board in place of the old.  Nothing else was changed/disturbed, but now the motors will not arm.
I've been through both the transmitter and vehicle configuration Wizards multiple times. Everything works properly through the primary control stick ([throttle, roll, pitch, yaw) recognition/identification, but the Wizard doesn't recognize the Flight Mode switch or any of the accessory switches, even though the transmitter configuration hasn't changed and it used to work prior to the frame repair.  In addition, the Wizard doesn't detect stick or switch movement to set the movement range or standard/reverse settings.
The Input Configuration screeen also doesn't detect stick input.
As I recollect, I had the same issue when initially setting up my system many moons ago, but have forgotten how I fixed it. 
My Tx is a Spektrum DX9 communicating via PWM with an Orange Rx.
Can anybody refresh my memory?

[f5soh]

While in Input tab you should see if moving the switch produces activity in top-right corner, if not, just double check the wiring.
After this simple check switch should be detected after running the Wizard, you may need to move the switch quickly between positions.

In addition, the Wizard doesn't detect stick or switch movement to set the movement range or standard/reverse settings.

That's a known behaviour if you skip the flight mode switch detection.

[TheOtherCliff]

Since you are using PWM, I suggest that you check the PWM input wires going into the FC.  Look for tiny tiny bent pins inside the FC connector or cracked soldering behind that connector.  They can be straighened with a #11 Xacto blade.  I also have tiny smooth jaw needle nose pliers that can fit in there (Craftsman) to straighten them out perfectly once they are upright.

Also, make sure the receiver to FC cable has continuity.  Check it with an ohm meter.

Also, did you replace the RC receiver?  Are you using a different transmitter model storage where maybe you forgot to enable the mode switch?

Test those channels by plugging a servo (or ESC/motor) directly into the receiver.  If you have signal there, but it does not show signal for those channels on the Input tab, you have narrowed it down to input connectors, wires, etc.

[HighAltitude]

Thanks f5soh and TheOtherCliff, it's working now.  As it turned out, one of the connections to the receiver was not seated fully.  The up side is that, with all the flailing around I did, I've reacquainted myself with the power and ease of use of Librepilot and the myriad nuances of configuring my transmitter to talk to its receiver.