Do you recall any changes made to the computer prior to the issue?
You may try these methods and check if it helps.
There is a possibility that internet settings are causing this error 438 to come up.
Go into your Internet Explorer and check out the Internet Security Settings. Make sure to set the level to
"medium high." If the level is set any higher, it can block the Windows Media Player from being able to download the license, causing Windows Media Player error 438 to come up.
Also in the Internet Security Settings, it is important to "run activex controls and plug-in." By enabling both of these settings, it should take care of what has been causing the error to occur in Windows Media Player.
Method 2: Reset the DRM store on the computer.
To do this, follow these steps:
a) If Windows Media Player is running, exit Windows Media Player.
b) Locate the DRM folder on the hard disk, and then rename the DRM folder to DRMbackup.
Note: By default, this folder is in the following location in Windows:
d) Follow the instructions on the Web site to update the security component of Windows Media Player. This procedure enables you to obtain new licenses for media content. You can also reset licenses for purchased content so that you can play that content
on a computer.
Note: DRM systems, such as Microsoft Windows Product Activation, maintain an internal hardware ID. This ID is based on the hardware configuration that existed when Windows was installed or when Windows Media Player 11 was installed. If you change
the computer processor or other devices, the hardware ID in the DRM system does not match the new computer configuration. When this occurs, DRM determines that a user has tried to move protected content to another computer. This behavior can also occur if
DRM-protected storage in the Windows registry has been changed.
Note: You must contact any third-party stores from which you purchased music to reset the licenses for that music. If you have copied CDs to protected Windows Media Audio files, those CDs must be copied again.
For your reference: When you try use Windows Media Player 11 to play a digital rights management (DRM)-protected media file, the media may not play