Some points to check.

Ensure everything (radio and car or truck) is turned off.
Ensure battery is charged

If everthing checks out, turn on you car or truck, the fail safe should apply full brake to your car or truck (if you have programmed your fail safe to apply full brake when there is no radio signal)
Turn on your radio, the brake and throttle should go to neutral position
Turn your steering left and right, pull and push the trigger from your controller.
If everything is fully functional, you are good to go.

On the otherside of things;
If there is no brake/throttle response after powering on your car or truck, your fail safe is inplugged from the receiver, or your fail safe is not programmed accordingly. Another cause is your receiver battery is dead.
If everything checks out fine from your car or truck, turn on the radio, if car or truck does not respond to the controllers input, check the battery level of your radio, check the receiver/transmitter cystals maybe one of the got loosen, try using a different set of crystals.

Worse case is that your failsafe needs replacement or there might be frayed wires. Check all your electronics connections, wires and its functions.