How can i remove/delete digits in the beginning of a string ?

You can even try extension functions:

string sample = "2. hi";

string result =
        string.Concat(
            sample
                .SkipWhile( char.IsWhiteSpace )
                .SkipWhile( char.IsDigit )
                .SkipWhile( ( c, i ) => i == 0 && c == '.' )
                .SkipWhile( char.IsWhiteSpace ) );