The problem is competing software wanting to open the same file types, and add to that we are always installing/uninstalling software, sometimes Windows appears to just 'give up the ghost'.
1] Open the application you are talking about, go to File > Open and navigate to one of these files of this file type and open it.
2] Instead of trying Folder Options, find a file of this file type, right click and select Open With, and select the application that way.
Do either of those work?
Also the application itself may have options to "Associate this application with these file types", but I can't say since you don't mention what app this is.
Do other people find that sometimes the whole system or process of telling Windows to use a specific application to open a specific filetype just seems to freeze or lock ?
e.g.I've just updated an application I use constantly, and removed the older version, and the files no longer seem to be knowing 'whose they are'.
So I've been through the familiar process from Control Panel,/Folder options etc, but even though I browse to the exec file and select it, when I get back to the box with the 'always use this application' checkbox, the selection has not taken effect. The name is not even in the list.
I've rerun the installation process for the application, and rebooted, with no effect.
Any thoughts, anyone ?