DSLR Nikon D3100 flash is too strong?

I don't know what i did but now my flash is way too strong when i take pictures on P/S/A/M

Is the flash set on manual output?

PSAM? That's everything! Read the manual to figure out the setting but in the mean time, simply step back.

Sounds like it's time to read your owner's manual.

You can reduce your flash intensity. That will definitely help.

Hold the exposure compensation and the flash button pressed. You should then see in the viewfinder the flash exposure compensation value. Make sure that it is set to ±0 by turning the thumb dial. It may be set to a positive value, which instructs the camera to use more power for the flash (and a negative one would instruct it to use less power)