If starter is not working, check that the battery is in good shape....
12.5 volts at rest...not less than 10 volts while cranking, about 13.4 v while running...if you get it to run!
Check battery contacts are clean and tight.
Check Negative battery lead going to chassis is clean and tight.
Check strap grounding engine to chassis is clean and tight both ends.
Check connections to solenoid/starter are good.
Try start in Neutral instead of Park
Check Fuse #8 40 Amps under the hood is good.
Swap over the Starter Relay under the hood with an identical one nearby.
Remove the Starter relay and identify female pin 30 and 87 inside the empty socket
With ignition On and in Park or Neutral
briefly jumper female pins 30 and 87 together...engine should turn over and run if Fuse #8 is OK.
This above procedure overrides the Ignition Switch and the Park and Neutral interlocks.
If the engine turns over OK then the Actuator Pin Assembly is probably broken....lots of hits here on how to replace it or get back to this post to get more info.
Check under your floor carpets for any major water entrance.
The ECM connectors could have gotten wet....dry them off with a hairdryer.
Bet you it is not the ECM...if I lose the bet then your check is in the mail...trust me!
The brake switch could be a problem...as stated it cannot be removed and put back...new one needs to be fitted. Rather check this out via the Wiring Diagrams rather than throwing money at it. This has no connection to the Starter not turning over.