Mp4 Error & No Thumbnails

In windows 7 using windows Windows Media Player 12 & VLC media player
I have mp4 & avi & 3gp video files. My avi files open as default in Win media player & have working thumbnail preview images. My 3gp files open in VLC media as default & have working thumbnails.
Yet for the life of me I can't fix mp4 files. They have the win media player icon regardless of what player I set as default & are very limited to what I can edit as far as file associations. I think it is a problem with my codec packs because I found this forum after downloading & installing a few codec packs that change the problem(s)
Right now I have only installed K-Lite Codec Pack 1452 Mega & Windows 7 Codec Pack 4
This seems to be the best I can find but I did try StarCodec 2018 & X-Codec Pack 2 & vlc.codec.pack.v2
Each of them did install fine & I had to remove them to install the best 2 that I have now.
I even did find ADVANCED Codecs v1067 Shark007 & it would not install because of a registry permission error in Hkey_LocaL_Machine/software/Classes/.flv when fixing this error I found no way to edit .mp4 or even look at this part of the registry. Access is denied.
I have Default Programs Editor that will let me add a Play tab to the left click menu & set that play as any program I like & even set it as default, but the thumbnails are still broken.
If I use Control panel I can change mp4 file associations & set any new default program but the icon will not change nor will the menu listing change form "Open". It will just change what program "open" leads to.
I see this same problem in .wav files too that the icon is some yellow folder looking icon even if I set win media player as default. Under "set your default programs" I have win media player set as default & it seems to be set fine, yet still no thumbnail on mp4 files. I have icaros installed & it works fine to fix any video thumbnails, except mp4. I have Codec Tweak Tool working & see an odd bug, when I set the thumbnails the mp4 is unchecked & if I check it all my icons will refresh & if I set thumbnails again the mp4 is unchecked again.
I know my Folder Options need to set to "always show icons, never thumbnails" as unchecked.
I know Performance Options needs "Show thumbnails instead of icons" checked.
Still I see no way to get thumbnails working for mp4 files & I need to fix the left click menu every time I install a new video related program or uninstall such.
Can you help me to understand this problem with mp4 file associations & broken thumbnails?
It is the only file type I care to fix, because I use mp4s so much.
Is there any way to copy all mp4 related registry keys from my old laptop to my main PC?
I could check my old net book to see if it will show thumbnails, but if it did, I know of no way to copy that
Anything you can think of for me to try I will consider. Thanks