Media center will not find any .avi or .mp4 files

Hello Bing CISM
It is a new installation.

Hello Merete:
I have added video using the methods you have posted.  IT DOES NOT WORK!!  
The avi and mp4 files do not appear after I have told Media Center where to look.

Q1.) How do I force Media Center to find the the avi and mp4 files?
Q2.)  What is the best way to determine if the Media Center database is corrupt?

Does windows media player play your avi and mp4?
Is avi and mp4 added to windows media player files types
go to start all programs default programs associate a file type with a program
I have windows 7 x 64 professional and installed two codecs ffdshow and ac3 filter I also have divX  player installed.
Windows media player is part of windows media center
drag and drop an avi or mp4 onto playlist wmp does it play?
Your movies folder has been added to the libraries same with music
Your WMC on Movies?
click on the window
if you see no items added go to tasks settings media libraries as posted above
add folders for movies on this computer
then just tick them all
then use the down arrow to see the locations
click yes use these then wait wait wait if you have a lot and are on USB it takes a while just wait till the circle goes, as I haven't added video will let you know as mine are on USB

Hello Merete:

Yes, Windows Media Player will play the avi and mp4 files.
In the rectangle above the start button I typed Extension.
I then searched for avi and mp4 and made sure the associated program was Media Player.
I restarted Media Center.   I then clicked on Tasks > Media Libraries > Videos > Next > Add folders to the library > next > On this computer > Next then selected all the folders where the mp4 and avi files are located.  I did this about an hour ago.  

Then I navigate to Pictures + videos > Video library.  No videos are present.  

Since Windows Media Player can play the videos, what must be done to fix Media Center so it sees the videos?

Then I navigate to Pictures + videos > Video library.  No videos are present.  
donpick
Open Windows Media Center. Use the arrow keys to scroll to Tasks, then click Settings.
Select "Media Libraries," then click "Next." Select "Add Folders to the Library," then click Next.
Click on your user name and expand the + sign
scroll down to my videos.
 Is your video located in My Videos under your user name?
Use the + and down arrow or up arrow buttons to navigate and select the folders that contain the MP4 files you want to play
When finished, click Next.
Select "Yes, Use These Locations."Click "Finish.
Close Windows Media Center or wait a few minutes while Windows Media Center adds the folders to your video library.

Start Windows Media Center. Click Video Library. Click on the MP4 video you want to play.
divx avi

Hello Merete

I tried all the things you suggested.  Nothing worked.
Decided to reinstall Windows from the original disks supplied with the pc.
Then I immediately configured Media Center while in an administrator account.

This worked.  
Thank you for your help.

Thanks to all who replied.

Wow that was a huge effort, Maybe all you needed was to use the admin straight off?
I am the default admin on my PC did that at setup.
Good to see it's resolved enjoy your movies ;)