Can't delete folder in Windows 8

You can use command line utility Handle by Microsoft Sysinternals. It can tell you which process holds file or directory open, like this:

handle c:\mydir

This will show which process holds directory open, if any.

You can also use Process Explorer, but you will have to search for your file/directory using Process Explorer UI.

While this works, I still find it too complicated, because I use Far Manager all the time, and FAR is helpful enough to show list and offer to kill processes that hold my files open if I am trying to delete them using Far Manager interface.