When opening files from Word, Excel, etc. you are presented with (and have to wait long periods of time for a dialog window that says “Initializing the root folders to display.” After it finishes, browsing through items becomes painfully slow.
There is a problem with one of your mapped network drives. Or, at least one of them is either disconnected or awaiting credentials. If you reconnect the problematic drive mapping, or disconnect it altogether, this problem will go away and cease to slow down your workflow.
Here’s a KB from Microsoft if you’d like to dig in a bit further: https://support.microsoft.com/en-us/kb/833041