Basic one way hash to store a password C#
No, it isnt.

First, you only allow ASCII characters in the password. If I were to choose €¥≠≥≤©® as my password, it would probably be equivalent to choosing ??????? (7 question marks). Try it.

Second, a password hashing function must be slow. Otherwise it is too easy to crack the password.

Third, when you hash a password, you must add some salt to it. This has the effect that even when two people use the same password, the hashed passwords are different, so a possible attacker cannot group people by their passwords.

Fourth, if you print the hashed password and it contains lots of question marks, you are doing it wrong. Instead of converting the hash bytes directly to a string, you must encode them so that only printable characters remain. Typical choices for such an encoding are base64 and hex.

In every possible scenario, even in school, you should use an established algorithm like bcrypt or scrypt instead of inventing your own.