No power output from my generac 5000 power plus generator

Depending on how long your generator has sat in storage, you may have lost the magnetism within the rotor. You may need to magnetize the rotor by flashing the field, "exciting" the generator to start producing power.

Depending on if you have a brushless generator or a brush type of generator the methods are different.

Brushless generators are often the easiest to flash, all you need is a corded electric drill.
It is up to you to determine if you have a brush type or brushless generator.

For brushless generators, ( WITH ENGINE RUNNING ) simply plug your corded drill into any of the 120 volt outlets on the panel.
Connect something like a desk lamp to another outlet as an indicator of success. Turn the lamp switch to the on position. With the "trigger pulled" on the corded drill, spin the chuck with your other hand. If all it needs is an excitation, the small amount of power going "back into the generator" from spinning the drill chuck will excite the generator. Feel free to try both directions on spinning the drill chuck. Normally it won't take but one or two good hard spins to get things going. Your desk lamp might light up rather quickly if you are successful. If after about 3 or 4 attempts with this simple procedure you still don't have an indication of power, the problem is most likely something else.

If you find some other component that failed, trying to procedure above might be necessary after the part replacement. Again, the rotor might still have lost it's magnetism.


FOR BRUSH TYPE GENERATORS -
Coleman Powermate Generators are easy to excite, use the info they provided for their generators on the page link below. Most all brush type generators are excited in similar fashion. DO BE CAREFUL and if you don't know what you are doing, DON'T try this. Find a qualified repair shop.

https://www.arkansas-ope.com/CP_GEN_EXCITATION.html

It is possible that your voltage regulator is shot but before purchasing the volt regulator try flashing the fields first and make sure the brushes and rings are clean.