MPG Files No Longer Listed in WMC Video Library

[Tntsotb]

I am running a W7 64-bit system.

Until recently, I could select WTV, MP4 and MPG files to play through WMC Video Library.
Now, only WTV and MP4 files are listed in WMC Video Library.
The MP4 files are all still present, and I can play them with WMC by selecting them through Windows File Explorer.

What I have tried includes:
Deleted and rebuilt system index, including drive upon which video files reside
Deleted and then added video libraries through WMC Media Library menus

Any help would be appreciated.

Thanks.