Alienware 17 R4 will not play iTunes videos

I assume they currently play ok from iPhone or iPad?

Is this machine authorized?

Can you get to your Account details in iTunes?

So, you are streaming these down, or you are playing downloaded copies?

These movies are truly in iTunes? Or, are they in a linked account (like Disney Movies Anywhere) ?

This is a shot in the dark as I haven't used iTunes in some time, but you can try installing DirectX 9 - I would not be surprised if Apple has not updated:

Download DirectX End-User Runtime Web Installer from Official Microsoft Download Center 

I assume they currently play ok from iPhone or iPad?  iPad pro plays them fine

Is this machine authorized? Yes as far as I can tell

Can you get to your Account details in iTunes? Yes

So, you are streaming these down, or you are playing downloaded copies? Have tried both ways, same result

These movies are truly in iTunes? Or, are they in a linked account (like Disney Movies Anywhere) ? They are all iTunes movies

Tried running iTunes in safe mode,no change there.... I am at work and bored anyway so I did a full wipe and restore of the laptop.

Install iTunes and the movies play fine, there is a large group of updates it wants to do(Windows) going to install them one at a time to see which one breaks iTunes, two updates are for the display and video card the rest look like security patches.. Will update in a few days, this may take some time doing them one at a time..

When a program fails to function properly you can access the software from "Programs and Features" in Control Panel and select Repair. Most but not all programs will allow you to repair their software from the Programs and Features list.

The most recent iTunes update caused some issues for me as well and the repair function restored iTunes. I believe the problem was with one of the iTunes services not being properly set during the update.

Try disabling Direct3D acceleration in QuickTime.

Open your QuickTime control panel (either via the Control panels, or by going "Edit > Preferences > QuickTime Preferences" in the Quicktime Player). In the Advanced tab, uncheck Enable Direct3D video acceleration:

Good work. Good troubleshooting. I would be interested to see what you discover.
 
Actually, I'm surprised how poorly iTunes and iCloud for Windows works on Windows-10/64bit. In my personal experience ... "barely working" and "breaks easily" are good ways to describe it. Still can't get my Photo Stream to work reliably on my Windows machines.

Right now it looks like the driver for the display panel on the laptop is the culprit, I rolled it back and can now play the movies.

A bit of a slow process, I have a few more programs and updates to install.

After that if they are still playing, I will update the display panel driver again and see what happens..

Take a full-system (all partition) Image Backup (with Verify on) while system is still working. Macrium Reflect Free v6.x would work.