I am having an unusual problem. I have always been able to drag files and folder from my desktop or explorer to the solution explorer in visual studio and add the files to m
I also cannot drop files from the explorer onto Visual Studio when it is running in admin mode.
But please try opening 'Add / Existing Item ... ' from the Solution Explorer / Manager context menu in Visual Studio and drag and drop files and folders from that window.
Works on my machine with Visual Studio 2012 ...