Video and Music thumbnails not showing.....

Ive read this is a windows 7 problem but all my mp4's have the usual default image instead of what they used to have when I first downloaded them. Did the thumbnail location change?
I did, at one point, install a new media player which became my default for some reason, I corrected that problem but all my mp4 thumbnails vanished after I returned media player as my default...whats the deal here? I tried clearing and resetting the thumbnail cache, I also tried rebuilding the icon cache as I had read on these forums that it might help.
These were fruitless...I seek advice, thank you very much. It is most appreciated.
From, Gary

First downloaded them in Windows 7? Windows 7 doesn't come with native mp4 video thumbnailing, so you would have had to download a video player or codec pack that had the proper codecs for thumbnailing. When you removed that media program that allowed thumbnailing, you also removed the codec for thumbnailing.

Try the Shark007 codecs. I've been using them for a long time now and they provide all types of thumbnailing for explorer and integrate into Windows media player so you can play most any file through it.

You will need to download the regular codec pack for Win 7, and then the 64 bit components (in this order) since you have an x64 system:

Shark007.net - Windows 7 Codecs - WMP12 Codecs
and
Shark007.net - Windows 7 x64 Codecs - WMP12 Codecs

Download and install in that order. Open the x32 program as admin, click suggested settings, close it, and re-open as regular user. Do the same thing for the x64 program. You should be all set with thumbnails after that.

Thanks it's was very helpful, now all video thumbs is working included .mkv