"SQL Server does not exist or access denied"

If you are facing

1]Error:- server does not exist or access denied

2]Error :- Changed database context to 'master'

3]SQLSTATE:0012A4D

Try out the following Solutions

1]Check the server name If you are providing this server name as connection string in the program 

then specify

hostname\\sqlexpress; as server name

instead  only hostname or hostname\sqlexpress.

2]Open port through the firewall

          Add port number (1433) and name in firewall

3]Open Run and type cliconfg
            select TCP/IP and enable 

4]Enable TCP/IP port

             Microsoft SQL Server-->configuration Tools-->SQL server configuration Manager

Connection string for the sql server 2008 is as follows

If only TCP/IP protocol is Enabled then provide the following string

"DRIVER={SQL Server};Provider=SQLOLEDB.1;server=hostname\\SQLEXPRESS;DATABASE=Database_name;";

If Shared memory ,Named Pipes are also enabled then

use network=DBMSSOCN; argument in the connection string

"DRIVER={SQL Server};Provider=SQLOLEDB.1;server=hostname\\SQLEXPRESS;network=DBMSSOCN;DATABASE=DatabaseName;

network=DBMSSOCN 

to use the TCP/IP protocol even if the Shared Memory or the Named Pipe protocols are available.