Warning: mssql_pconnect() [function.mssql-pconnect]: Unable to connect to server: mycomputer\SQLEXPRESS
-first check if this is running in your sql browser.
-check if the tcp/ip is enabled.
if you can make the odbc then test it. create a php files then check if it is running like placing a code
$myconn = mssql_pconnect('hstname','user','pass','db') or die(unable to connect sql);
from there you can check if your computername\SQLEXPRESS is functioning. Use MSSQL 2012 its better and easier than 2005.