It probably isn't the circuit breaker. The magnetic field has likely weakened (especially if the generator has not been used in a while). The magnet can be "flashed" by running a current through the generator briefly. The easiest way to do this is to plug in a motor and spin it backwards (by hand) while the generator is running (e.g. an electric drill). The drill acts as a weak generator when you put the energy into it by spinning it.
A previous answer I gave to the same problem...
---
Look in the manual. There is likely something about field flashing the
magnetic field. According to the Briggs and Straton web site (similar solution for all generators), the easiest way to do this is to.
1) start the generator
2) plug an electric drill into the generator (without drill bit)
3) make sure drill is set to forward direction (if a reversable drill.
4) pull the trigger on the drill.
5) If the drill does not start, spin the drill's chuck in reverse [clockwise (When looking down at the chuck from the drill bit end). Spin counter-clockwise if holding it like a pistol and pointing away from yourself].
6) Do this several times (hard) until the the generator will kick in and suddenly make the drill spin at full speed.
Be careful not to drop the drill or poke someone with it as you celebrate success.