Has this radio system ever been used before? Been in a crash? What is the radio system? A lot of unknowns.
If no metal-metal contacts first try a different battery, then, bypass switch with battery directly into receiver, then unplug servos one at a time to see if problem goes away, could be a bad servo, then what is left is receiver.
I am assuming of course you do not have a spare receiver.
Once you eliminate everything else what remains must be the truth.