As I entered a program (a game) from windows, the screen distorted(concaved become a "obese" screen)?

Hi.

My computer screen is normal and almost fit my monitor screen's size, but as I entered a program, which is a game, the screen suddenly distorted - not literally distorted, it is just the side there concaved, that is longer at the middle but shorter at the upper and lower side, as if a obese man.

Why is this happening, I encountered this problem when I change my Screen Refresh Rate to a higher herzt.

Thanks!