Files to open with default applications

So my windows won't open certain files with their default applications. Double-clicking .html files won't open them up in Firefox, and neither will .mp3's in Foobar2000. I also noticed that I can't drag and drop those files into their respective applications straight from explorer like I used to be able to, but I can open (and drag and drop) if I use the application's built-in 'file -> open' command, just not from explorer...

The files are set to open in those programs by default.

Any help would be appreciated.

You can change the default application by right clicking on the file and choosing Open With... and then expand the list of programs. Highlight the application you wish to open that file type, check the option for "Always use this selected program to open this kind of file" and click OK. This should lock in the default app.

As far as the drag and drop, I'm not sure on that one.