Display formula problem

Hello all,
I use Mathematica for several years without any problem.

But since last week, I can’t write correctly formulas on Mathematica. For a simple example, if I write $frac{1}{2}$ by typing $1 /2$ , a small retangular appears instead of the operator $/$.

And if I declare a CDF of the normal distribution, I just got an unreadable formula.

I don’t know why. Perhaps because I has modified the Windows system last month?

Do you have any idea to fix this?

Thank you in advance.