YOU SAID:
school shouldn't be open today
INTO JAPANESE
学校は今日開いてはいけません
BACK INTO ENGLISH
School should not open today
INTO JAPANESE
今日は学校が開いてはいけません
BACK INTO ENGLISH
School must not open today
INTO JAPANESE
今日は学校が開いてはいけません
BACK INTO ENGLISH
School must not open today
That didn't even make that much sense in English.