I reinstalled my friend's machine. She is missing a DVD decoder now and cannot play DVDs. Tried downloading the K-Lite Codec Pack and VLC player, but when she plays a DVD with either of those, the video opens in a full screen on her monitor but then she is unable to do anything. She cannot navigate the menus, cannot start/stop/pause or adjust the volume. And more surprisingly she cannot exit the DVD program! Typically popping out the DVD from the drive will cause it freeze on the last frame played, sometimes it will exit the program and return to Windows.

This is a laptop computer with a blown out back light. She has an external monitor
connected to her VGA port on the back of the computer. The only logical explanation I could come up with for this was that because of her external monitor, it was
displaying the video on the "2nd" monitor and then leaving the other "1st" monitor
free for controls or whatever. (Cannot see the "1st" monitor -- lamp is out!)

Does anyone have suggestions as to another free DVD decoder? I have already told her how to request the OEM CDs from Dell and have tried researching for the DVD decoder on Dell's website.

Ok, that's weird.
Try setting the primary display as the external one.
This option is found in the Display Settings.

Also, update the driver for your DVD reader/writer.

Please get back to me if this works ;)

Ashley, Media Player Classic is included with the K-Lite Codec Pack. Tried it, same problem and so here I am. I will try updating both drivers and let you know!

right click on the screen when dvd is playing usually gives dvd controls!

Caper, sorry I did not make it clear in my original post, but she is not able to do that. She is not able to control any part of the DVD playback once it fills her screen. No buttons, no mouse, no keyboard, nothing.

I was able to secure the original Dell CDs for her model computer and we will see if using the programs provided by the manufacturer help out any....