Don't confuse custom-burned data DVD's with movie DVD's.
If you can't play movie DVD's then it is a missing CODEC or ASPI layer. Files are still accessible.
If your DVD device is having trouble reading from DVD in general(other than scratched surface or poor copy) then the problem is more likely of hardware nature.

First thing to do is get some free tool like http://www.cdspeed2000.com/files/NeroInfoTool_403.zip
that would give you some in-depth info about your hardware and software, along with the disc in question.

First thing that comes to my mind to remedy this is firmware upgrade. Almost every optical drive has some flaw which are fixed by upgrading the firmware.
You must know EXACT model of your optical drive and Firmware version. Easiest way to learn this is by that tool above.

In the "drive" tab you will see supported read and write features (and notice the number of different CD/DVD formats!) and in the "general" box at the top right corner you can see firmware version.

Also, insert the DVD in question and click on the "disc" tab to see some details about that disc. "Type" should be DVD-ROM or DVD+ROM.

If you're not confidant with flashing the optical drive, you can always post here drive's specifications (manufacturer, exact model and firmware version) and I'll see if there is anything there can be done.

Thank you for your help.

I installed the Nero Info Tool.
Here is the info that I see for my dvd drive and the disc:

HL-DT-ST DVD+RW GWA4164B
Firmware: D108
DVD+-R/RW DL Recorder
Supports all dvd types
The tool recognizes one of the files on the dvd (where none could be read in Explore), the disc is a dvd-r

Let me know if more info is needed and where to look for it.

Thanks again.

I've looked it up. It is LG product and there's no firmware upgrade available.

I've also learned that... well, read this and you'll be the judge:

http://forums.us.dell.com/supportfor...sage.id=109223

There is one workaround for unsupported CD/DVD formats.
It requires burning software like Nero 7 and deamontools-like virtual drive.

Basically, you have to copy DVD image with, for example, Alcohol 120% to your HD and mount that image on the virtual drive (also in alcohol 120%). You can download trial version here:

http://trial.alcohol-soft.com/en/

You will have to enable virtual drive in Alcohol settings.