Most probably you may have to change the way that you saving your username/password.
have you use any password encryption method? if no try below,
create a column in your table to store password and set its data type to varbinary(500)
if you are using stored procedure to save your data you can save password by encrypting like below,
DECLARE @Plaintext nvarchar(500)
SET @Plaintext = @in_Password
set @Plaintext = HashBytes('MD5', @Plaintext)
@in_Password is the password field that you provide. and insert it as
INSERT INTO Users
(Password)
VALUES
(@Plaintext)
OR
INSERT INTO Users
(Password)
VALUES
(HashBytes('MD5', @in_Password)
in user login event compare password as
SELECT * FROM User
WHERE UserName=@UserName
AND password=HashBytes('MD5', @password)