If you are able to hear audio from CDs and DVDs on your computer, but cannot see any video from the DVDs, there are two possible problems. If you have only recently installed DVD playback software onto your computer and have never been able to view DVDs, your system may not meet the software's requirements. Visit the DVD software's website to find out what the system requirements are and whether your computer meets them. If not, you will either need to upgrade your computer to meet these requirements or find a different DVD playback program that is compatible with your computer.
The second problem that might cause you to only hear audio from CDs and DVDs, but not be able to view the DVD videos is that the DVD player's drivers need to be updated. To check the driver status and look for updates for your computer's DVD player, go to the Control Panel and open Device Manager. Expand the DVD drive and right click the DVD player device. Select Properties and check the status to see if the device is working properly. Then, go to the Driver tab and click Update Driver. Select to search the Internet for updates. If Windows is unable to find an update, visit the website of the DVD player's manufacturer to check for and install any available driver updates.
This should also fix the problem if you can see video but not hear any sound, and may fix the problem of the DVD player not working at all.

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If you do not see a DVD player in the Device Manager, either there is not one installed or it has died and needs to be replaced.