When you move your DotNetNuke 7 instance from Windows Server 2012 to a new Windows Server 2012 R2 instance, you might end up with poorly rendered skin. This issue relates to a situation where the related Telerik Script Manager is not properly loaded.
Querying the affected website with Web Page Test showed, in this case, the query for Telerik.Web.UI.WebResource.axd resource resulted in a 404 HTTP error.
Searching the web resulted in a variety of proposed solutions to this issue. In this case, the solution is as follows.
The Telerik.Web.UI.WebResource.axd handler must be added to the system.webServer/handlers section of the web.config.
If the system.webServer node does not have a handlers node, add it.