Best thing to do is to isolate the problem. Nitro Vehicles only have 4 things that are electric:
-The Receiver
-2 Servos (one for steering & one for throttle)
-Battery Pack to run the above 3 things
If you not getting any signal at all to the steering & throttle servo, then it could be just your receiver.
If you are getting signal to 1 or the other then one of your servos could be dead.
All this is assuming your battery is charged and is not fried.
A new receiver at worst is $80 for top of the line models depending on your transmitter. You can pick something up for $40 bucks.
Servos can run up to $130 per servos for top of the line models.
Again, you can find some cheapos for $30-40 bucks each.
Most problems are with the receiver. Unless you heavily protected it with a balloon or cover of some sort, the elements fry this thing quick especially if you are bashing your vehicle.
Any moisture or water get to your rig?
Also, sounds dumb, but always check your battery pack and make sure it is charged.
Good Luck.