Hey, you should specify the userid and password in your connection string you can use one of the following:

connectionString="server=localhost;uid=sa;pwd=yourpasswordhere;database= yourdatabasenamehere";

OR use this in your web.config:

<connectionStrings>
<add name="DatabaseConnectionString" connectionString="Data Source=YourServerName;Initial Catalog=YourDatabaseName.MDF;User ID=sa;Password=YourPassword" providerName="System.Data.SqlClient"/>
</connectionStrings>
or if you are trying to put the paramerts dynamically from some controls use the following:
string connectionString = 
               "server= " + VarServerName + 
               "; uid=sa;pwd=" +
               varPassword + "; database= " + VarDatabase;
hope this help 
thanks