The green bar is often caused by the OS loading and preparing thumbnails. It can also be caused by slow network connection. You can take care of the first issue by changing the following setting:
Explorer> Organize> Folder and Search Options> View> Always show icons, never thumbnails
This will tell the computer to open your folders with icons for each file instead of thumbnails which is the problem that causes the slowness.
Note, if your Explorer crashes, you won't be able to open another instance of it until you kill the explorer process. So, it is a good idea to run every Explorer in its own process, you might want to set the following.
Explorer> Organize> Folder and Search Options> View> Launch folder windows in a separate process
Hope this helps and regards