Cannot open database requested by the login. The login failed

hi!
i have create a vizual c# program linq to sql ..when i whont to open the databse from vizual i have this error ...
Cannot open database requested by the login. The login failed. Login failed for user
please can someone help me ??

THNX )
what do you mean with the kind of connexion ??

mmmmm i dont know
when I open the database from sql it notopen to visual and vice versa
and when i do the add student on the program, the student is adde to the datagred..but not added on the database (

mmm the situation is this :


i have to create a desktop program ,and im usin vizual c# 2010 and sql server 2008 both expres edition .
now i create the code and the connection ...bug the program doesen add the student on the database only on the datagrid
if i open the database first on sql server i cant open it on the vizual C # ..and the error is : Cannot open database requested by the login. The login failed. Login failed for user
but if i open the database first on vizua c i cant open then on the sql server ..and the error is : The database is not accessible (ObjectExplorer)