Problems with Installation of SAP NW 2004s Trial Version from CD

Hello,

preparing the installation by execute the start.bat the wizard sends the message

"The wizard has detected an already existing SAP system NSP on this host.

Uninstall first".

But no SAP-System is installed. In Folder Software there is also no SAP-System to uninstall. The Folder SAP in Folder Install Shields has already been deleted before starting installation.

How can I find out what I have to delete too so that the installation is starting ?

Thanks

Andreas