Hello!  First I would go here to get your drivers.  Then if your computer qualifies you can download the Windows Image from here.  Follow the instructions carefully and you should be set. 
I've finally given up on my Windows 10 upgrade.  It crashes a lot, a Win 10 update comes out and then it only crashes some, then another comes out and now it crashes a lot and won't talk to my thermal systems half of the time and that leaves my fans all blasting at full.  I only found out after my upgrade that my Alienware Aurora isn't certified compatible with Windows 10. I can't run the Dell diagnostic to see if I actually have any hardware problems because it crashes every single time that I run it.  I'm hoping that going back to an earlier version of Windows will allow it to run again and see if my hardware is fully operational. It has been too long since I've installed Windows 10 so I can no longer revert so I have to get a previous version and install it.  Since one of my issues is talking to my Alienware hardware (when Windows does stay up), being able to do so is important to me.  My problem is that no where on the support site can I find a place to download the Alienware apps (AlienAdrenaline, AlienFusion, AlienFX Controller, AlienFX Editor, Alienware Command Center, Thermal Controller).  When I reinstall Windows, I'm going to have to reinstall all of that as well or lose it. Does anyone know where / how I can get the Dell and Alienware software to reinstall? Thanks.
Install Win 7 over Win 10... where to get Dell & Alienware software to 
reinstall?