I am using a square d panel qo type. I am getting 240 volts across the two hots in but only 120 out of the 240 breakers, this happened all of a sudden, what could be wrong? I have double checked all the connections.
John

Bad main breaker? That's about the only thing it could be.

Did you check the voltage at the breaker buss?

Okay,

You need to help us here.

For example, when you say you get "240 across both hots", are you referring to the Main Breaker?

If you are measuring the output of a 240 V Branch Circuit, such as a range or electric dryer, and only seeing 120 volts then you probably need to replace either one of the bus bars or the entire panel.