Setup of SQL Server 2008: Restart required but I have restarted

Hello,

I have tried to install SQL Server 2008. I cannot install, because I get the errormessage the prerequistite "Restart the computer is required".

But every time I restart my computer and try to execute the setup of SQL Server 2008, I get the same message, I have to restart the computer.

I cannot install the SQL Server 2008.

What can I do?

Thanks