This just started a few days ago when renaming a picture file I downloaded when after clearing the title and renaming it said "this file extension may no longer be found after changing." I changed it anyway and after could not open it and the thumbnail just looked blank in Explorer. Also after I downloaded and changed the names of 2 You tube how to videos and got the same message,which I had never gotten before by the way, and after changing them they also had blank thumbnails in my videos folder and could not be opened due to no file extension showing. Freaking out I then looked for my other "how to" videos long ago downloaded and could not even find them in my video folder or by just searching in start menu search. They and a lot of other videos and pics seem to be gone or not searchable. I checked my folder option settings and hide file extension settings is unchecked as it has been for a long time and I understand what that means but these other videos I renamed long ago have still been able to be found and viewed after renaming the until now. Like I said, only 2 days ago when I tried to rename this one picture file and after those 2 You tube how to video files has this Explorer window opened saying "do you really want to change the file extension name and if yes you may not find it." Why then have I been able to do the same thing for months and even view these videos but now they no longer even show. Debating to do a Windows backup restore from last week or a system restore point from but I'd rather see if anyone has any other ideas. Also not sure this would fix things as I have had access to these videos and pictures in the past after changing names. My biggest issue is I do understand the hide or don't hide option with file folders, what I don't understand is why files that been changed and viewed in the past no longer show up and file name changes from just two days ago now suddenly show a warning notice from Windows that never showed up before.I also recently updated Windows Media Player and had it set as the default player by accident for the last few weeks but other than not being able to play certain formats I'm not sure what that could have to do with my files being missing now. Set Potplayer back as my default and have used VLC media player before that. P.S I have made no changes to the registry myself but I do use CCleaner from week to week. Should I try to restore a saved change from that cleaning from a few weeks ago? I save them in my Documents folder but have never had CCleaner cause me problems in the past. Last thing is I checked the folder location for these 2 recently added videos that I couldn't access before they disappeared altogether and it said they were in folder /music/videos/ for whatever that's worth. Seemed kind of weird but have had other players try to combine music and video files before but this after just saving them with Firefox's Downloadhelper extension I have used for years. Grateful for any and all help. Tom.