Sadly it is sometimes the nature of Windows that DEX and other programs do not work.
If DEX does not start, a quick fix can be to delete the settings.
First click 
in the Ribbon menu Panels->Panels command group. This will restore all the panel settings.
If this does not work:
Try deleting...
C: \Users\XXX\AppData\Roaming\DEX Software\DEX\Settings
where XXX is you.
1.Next, make sure you have the latest graphics card driver. See Update the Graphics Card Driver
2.If it still is not working Manually Removing DEX and then install it from https://dexpcb.com/Download
3.If it still is not working Reinstall .NET
4.If it is still not working use Restore Points
5.If things are still not working I suggest trying a different graphics card.
6.Finally if things are still not working, backup all your data and repair Windows using the Windows DVD that came with your machine.
Update the Graphics Card Driver