What kind of mic?
If it’s a dynamic, then the incoming signal will be reasonably low by nature and having to turn gain up to get a clear signal (within reason) isn’t very strange.
OTOH, if your mic is an electret design, you probably have to turn on the H4n’s phantom power in the menu in order to properly power the mic.
It’s also possible that cable or mic or even the unit itself is defective.
All possibilities that require traditional gain structure troubleshooting to track down and solve.
Good luck.
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