I have tried creating a validation rule on case with the below condition. When am trying to test, it was working fine but it was throwing an error even when all the required fields are filled and also throws an error message even when trying to close a case. 
AND(
$User.Country ='AB',
ISPICKVAL(Status,"Closed"),
OR(
ISBLANK(Account.Name),
ISBLANK(A),
ISBLANK(B),
ISBLANK(C),
ISBLANK(D),
ISBLANK(E)))

Exact requirement is when status of the case is closed all the fields A,B,C,D,E fields are mandatory to fill through validation rule