So lately this problem for me has gotten out of hand. After some research on the web and a couple of Microsoft articles here's what you can do to fix this issue:
1. Open Control Panel
2. Select File Explorer Options
3. Click on CLEAR at the bottom beside of "Clear File Explorer History".
Apparently bad data in this windows can cause Explorer to freeze up.
One more thing. If this doesn't work then change the option at the top of the File Explorer Options to open to "This PC" instead of the default which is quick access.
Hope this helps if you're running into this issue.