Having Problems, Keeps Denying That Im The DBO

Ok. I tried this in the other part of the forum and i had about 100 views but no help, and no point in the right direction so i figured i would try here. PLEASE admins if this is the wrong forum for it, please move/direct me to the right one so i can get help. This is very frustrating

Im using Visual Studio 2008. I have the Sql server express that is install with the Visual Studio 2008. I created a new website, created a new database under app_data. Try to create a Database Diagram after making 2 tables and this is what happens.

"This database does not have a valid dbo user or you do not have permissions to impersonate the dbo user, so database diagramming is not available. Do you want to make yourself the dbo of this database in order to use database diagramming?" (Yes, No, Help) so i click yes

i get "This server does not have one or more of the database objects required to use database diagramming. Do you wish to create them?" (Yes, No, Help) i click yes (Mind you i am running visual studio 2008 as an administrator.

I get the error message. "Could not obtain information about Windows NT group/user 'BCOMPUTEROwner', error code 0x534.

My operating system is Windows Vista Business.

Please any help, point in the right direction. It would be greatly appreciated. Thank you