Asp.Net web application administration cannot connect sql server?

[Guest]

I've SQLExpress installed and running on my PC. The security tab still shows:

"There is a problem with your selected data store. This can be caused by an
invalid server name or credentials, or by insufficient permission. It can
also be caused by the role manager feature not being enabled. Click the
button below to be redirected to a page where you can choose a new data store.

The following message may help in diagnosing the problem: Unable to connect
to SQL Server database."

What I missed?
TIA

 

[Guest]

I just found that the aspnetdb.mdf was removed from my app_data folder. Can u
create an empty db with the same name and put over there?

 

[Guest]

Now the error is

An error has occurred while establishing a connection to the server. When
connecting to SQL Server 2005, this failure may be caused by the fact that
under the default settings SQL Server does not allow remote connections.
(provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance
Specified)