thanks...to both..Manish & Brijesh

may be this will help you

1.Testing without entering any username and password
2.Test it only with Username
3.Test it only with password.
4 .User name with wrong password
5. Password with wrong user name
6. Right username and right password
7. Cancel, after entering username and pwd.
8.Enter long username and password, that exceeds the set limit of charectors.
9.Try copy/paste in the password text box.
10.After successfull sign-out, try "Back" option from your browser. Check whether it gets you to the "signed-in" page.

1)Test When login form get openend default focus should be set
on User Id text box.
2) Test leave all the column blank

3) Test for Min and Max Limits for User Id and Pwd Text Box
4) Test whether Pwd text box allows user to Copy and Paste
the entered text in the Pwd text box (It should not allow)

5) Test it only with username

6) Test it only with password
6)Check for the UserId and Pwd field's case sensitivity.(It 
should be case sensitive)
8)Check the functionality after click on Ok and Cancel
Buttons.