Try this. Change the view to list or details. That way Windows File Explorer does not have to slog through the files checking for thumbnails, updates to same and more.
The BIG CLUE is the dialog boxes which for most things are in list view.
At some point in time (I cannot remember when, but I do not believe it was between Windows updates), the Windows Explorer on my computer started acting strange. Whenever I try to open my documents, C drive, Control Panel, etc., at least 10 seconds pass before it actually opens. The delay lessens the longer my computer has been on. At worst, explorer.exe will be "not responding" and has to be restarted, which means I can't do anything for a minute or so while Explorer sorts itself out. For some reason, these problems don't usually occur with things like Save As dialogue boxes. I have run virus scans and detected nothing. The rest of my computer is not this slow.
Dell Inspiron 660
Intel Core i5-3340 CPU @ 3.10GHz
8GB of RAM
64-bit Windows OS
P.S. Tell me if this post is in the wrong category. "PC software" just didn't seem right.