Are you sure that your DB is working fine in windows 7? Coz Oracle 10g wasn't working with vista when i tried. If database is connected through sqlplus or any other tool then make sure your crystal report connection is valid.

I have managed to get Crystal to work by downloading a newer version of 11g client install with ODBC drivers which included Microsoft ODBC for Oracle.
I can now load and run most of my reports.
I have another problem - when I have a report that requires a parameter, I get a Script Error - the URL refers to a file prompting1.html in c://users/xxx.DOMAIN/AppData/Local/Temp which when searched for just looks like the parameter window.  If you try to enter a value, it repeats the error window and only pressing ESC gets you out of the loop and then the report does not return any values as the parameter has not been accepted.
Any ideas?