i wanted to validate password in login form which i created in c#.I entered password in database in lower case but in web form when i enter password in upper case it takes that password and goes to next page. It must validate only lowercase password when i entered password in lowercase in database and show error'invalid password ' when enter a paassword in uppercase.

The problem might be the way your database makes string comparisons. Depending on what database you use you can probably set it to do either case sensitive or case insensitive comparisons. Also check the password that your program is actually sending to the db to make sure it has the correct case -- are you sure your program is not converting the string to lower case?