error with sql server in c#

I debuged my programm and it worked properly,but now i face this two errors,

1- Unable to delete file "C:\Users\M.elecworld\Documents\Visual Studio 2008\Projects\SendSMS\SendSMS\bin\Debug\Database.mdf". The process cannot access the file 'C:\Users\M.elecworld\Documents\Visual Studio 2008\Projects\SendSMS\SendSMS\bin\Debug\Database.mdf' because it is being used by another process.
2- Unable to delete file "C:\Users\M.elecworld\Documents\Visual Studio 2008\Projects\SendSMS\SendSMS\bin\Debug\Database_log.ldf". The process cannot access the file 'C:\Users\M.elecworld\Documents\Visual Studio 2008\Projects\SendSMS\SendSMS\bin\Debug\Database_log.ldf' because it is being used by another process.


I want to make my reports with stimulsoft for the first time and ,also there I face this error when I wanted to connect to my Database.

my connection string in stimulsoft is below:
Attach DbFilename=C:\Users\M.elecworld\Documents\Visual studio 2008\Projects\SensSMS\SendSMs\bin\Debug\Database.mdf:Data Source=SUN-PC;Integrated Security=true

but when I test the connection it errors:

Connection error=A network-related or instance-specific error accured while stablishing a connection to SQL Server. The server was not found or was not accessible.Verify that the instance name is correct and that SQL Server is configured to allow remote connections.(providr:Named Pipes provider,error:40 - could not open a connection to SQL Server)