You are probably using the wrong DbConnection class.
If you are using Access then make sure you use OleDbConnection, not SqlConnection…and vice versa.
Alternatively you could be referencing your MDB file wrong. Here’s the proper way:
<connectionStrings>
<add name=“Videos” connectionString=“Provider=Microsoft.Jet.OLEDB.4.0; Data Source={0}App_Data\Videos.mdb” providerName=“System.Data.OleDb”/>
</connectionStrings>
public static string ConnectionString = string.Format(ConfigurationManager.ConnectionStrings[“Videos”].ConnectionString, HttpContext.Current.Server.MapPath("~/"));