In the recent DNN 7 releases, they have unfortunately made by default a popup greeting after sign in, that in theory would drive clients to signup for their spam.
Problem is (like lots of recent DNN features) that the “tick to never show again” does not work, and in some really recent releases, the popup goes crazy and does not allow you to progress into the site.
In other words, they killed their own product with spam crap.
Easy fix. Open the file in the web root, called: Default.aspx.cs
Look for this line: ManageGettingStarted();
Just throw a // before it to comment it out.
Save and restart the IIS site. Should fix it fast and for good.