Video files not showing up in folders

I'm having a problem using WMC to view my video collection. The individual folders are appearing in WMC video library but the folders are empty. The video files are .avi format and play just fine with WMP or DIVX player. I have an xbox extender that also sees the folders but the files are not there.
I've looked through this forum but I don't see an answer for this question.
Any help would be appreciated.
Windows 7 build 7229 x64

I am having the exact same problem! On another forum I wrote this:
"
I'm running Windows 7 RC. If I add a folder to one of my HDD's and use Media Center to include the folder in the libraries as part of Video everything seems to work fine. However, if I go to the video library in Media Center the folder and files don't show up.
If I use Media Player I do see the files that are in those folders. (So the library seems correct.) After that, still nothing in Media Center.
I've also tried to have Media Center just run through the file discovery (the pop up box that you get just after adding new folders to watch). This also had no result.
Does somebody have an idea?
"
It is also concerning avi's. The avi's that were in another folder while installing Windows 7 DO show up in the library and in Media Center.

Thanks for the help.
I re-installed the codec and all is fine.
Thanks again

Unfortunately on my machine the registry entry was already correct, so something different is happening. Perhaps I need to restart the machine.

mikinho said:

Did you install\uninstall a codec pack? If so, good chance you screwed up your perceived file type for AVIs.

Import this registry key: http://www.mikinho.com/wmc/fix/avi.reg. You made need to restart for it to take affect.

Thank you mikinho this worked a treat for me too. (Was worried about doing anything to the registry, as it is a brand new pc and not mine thought if it went fubar i'd just format and start again!)

Aclc said:

The above registry key worked to show all my avi files, but my mpeg files are still not showing. I solved this problem by watching the following youtube video:
[Tutorial] Installing Codecs and MKV support for Windows Media Center - YouTube

After spending weeks trying to figure this out, this worked for me. I uninstalled all existing codecs I had, and am only running the shark007 pack and registry settings.

Thank you!

In my case it was all .mp4's and some .avi's, and they had shown up in WMC fine for a while and one day suddenly disappeared. On the flip side some of the "suggested fixes" such as organizing the folders and running YAMM ended up not fixing anything, but made it better to use.