I've had this problem at three different locations since SW2011 SP3
When I click insert==>new component or File==>New, there's a five-to-ten second delay afterwhich the dialog appears as expected.
First thing I checked for was unresolved paths to the templates folder and I verified that there were none unresolved.
I also have this problem on a machine where my template path is sitting in a local folder on my harddrive.
I've tried opening all of my templates and saving them to the latest version but still the lag persists.
I re-use my template locations when I upgrade to new releases and I have a couple of subfolders in there. All told, I have maybe 20 template files.
What do you guys think?