I'm trying to use Excel Connector to import data into Salesforce. A colleague of successfully used it before and now I want to finish the job. Our Salesforce database already contains all our clients. When I connect with Excel Connector using the server URL https://www.salesforce.com/services/Soap/c/13.0 the list of accounts seems to be part of a sandbox database.
Is there maybe some user setting in Salesforce for my account that is set wrong?
That is the correct setting for connecting to a Production org.
If you did want to use it with a sandbox you would click advanced and change it to https://test.salesforce.com/services/Soap/c/13.0
Are you using the correct username and password for production? Have you tried forcing a logout first (Force.com Connector | Logout Session)?
edit
The credentials that you use to login to production should be different (username) from the credentials that you use to login to sandbox.
To double check that you are logged into production through the Force.com connector, first logout, then login again (e.g. by creating a table query). Then, in Salesforce production look at the user record and you should see the login history
If you see this "Apex Office Toolkit" under your production user then you are logged into Production.
HKEY_CURRENT_USER\Software\Salesforce.comin the registry to make sure there is no key called "Excel" there