avi files cannot be played successfully on iMac 10.7.5

I have a client who suddenly cannot play avi video files on an imac running 10.7.5 osx.

i am not a huge whizz on iMac so i was not able to see what the software was not encoding the video properly.

When they try to play the video it comes up with moving colour blocks on the screen, but no clear or even fuzzy picture.  you can also hear sounds but not anything legible.

is this something to do with codecs?

Can someone help me to solve this one at all.
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Tim LapinConnect With a Mentor Computer Consultant (Desktop analyst)Commented:
Also consider VLC.  It is both player and a collection of CODECs.  The Mac download can be found here:  VLC for Mac

A note about Perian:
 Perian will soon be discontinued.  Although it should work fine on Lion, its demise is something to keep in mind.
Download and install the latest free version of Flip4Mac:

Also, download and install Perian:  http://perian.cachefly.net/Perian_1.2.3.dmg (also free).

Between the two of them, they will install most codecs needed.
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mbellettyAuthor Commented:
I am pretty sure I did both of those and they did not work, but will try again with your links and see what happens.
Can you send us a link to one of the files he can't play?
Is he trying to play the files in his browser or in QuickTime player? If in a browser, which one?
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