When using Windows 8.1, start Internet Explorer 11 (IE11) as usual and you see the following:
The screen is blank (no home page). It is not possible to browse anywhere. Most of the gear menu's options are disabled (greyed out).
There appears to be a bug that after running the Developer Tools (press F12) the user policy gets messed up. If anyone reading this article has some more detailed information then please write in the comments, it would be really good to understand this issue more.
This is the best solution I've found. There do seem to be more (see the References below) but have a go with this first, it's worked repeatedly for me.
1. Press the Windows key and R to bring up the Run dialogue box
2. Type iexplore -extoff and press Enter (as shown above)
IE will load without extensions or add-ons.
3. Press F12 to bring up the Developer Tools
4. Press F12 again to close the Developer Tools
5. Close IE
6. Start IE normally (use your usual icon) and it should be back to normal