Why does half of my house have electricity and the other half doesn't with no circuit breakers poped?

as an electrician i would first check the main breaker with a rated voltage tester for voltage i would first ckeck the meter side by placing one tester lead on one of incoming phases or wire and place second lead on the other phase or other wire. i should read 240, or 230, or 220 volts depending on where the taps are in the transformer. if not call the power company. if it does read any of them voltages i would then check the load side of the main breaker by putting my leads on one breaker and the one right below it generally every other breaker is a different phase again i should read 240 volts or close. if not the main breaker may be bad. if you know what breaker or circuit its on you could test it by placing one lead on the screw where the wire is and the other on the neutral or ground bar here you should read 120 volts or close if not breaker is bad. it maybe as easy as tightening the screw or screws so shut the breaker off first and then tighten.