In ,
Jon typed:
I have a main power box outside with two 50-amp breakers
and one 30-amp breaker. A voltage test shows 120 volts
passing through them. Three of my six 20 amp breakers in
the inside box are not receiving any voltage. They did not
trip, just out of the blue for no apparent reason stopped
getting any power through them. The other three are
working normally. What is going on?

Since you have to ask, and that's the most dangerous place there is to play
around power, you should get a pro in to take care of it. You have a breaker
problem, loose wires or a break further up the line.