See if mskb #914277 How to configure SQL Server 2005 to allow remote connections helps

>Hardware guys just rebuilt a network C drive and I had to re install Sql Server Express.
>Now, only the Adminsitrator can access , else it gives a violation error.
>Is there anything else that needs to be done, either at the window level ,or
> the database level to give full rights to the database to users who are not
> administrators
>