It sounds like you have inadvertently downloaded CCleaner Browser, which has associated your files with the browser.
Almost all newly installed browsers will do this and reassociate how files are opened.
What can you do about it?
Have a look at this link, it talks about PDF files - but it is the same process for any other file that has been reassociated.
You just have to set the file association back to whichever programme you want to open those files with.
Once the association is set back then the icons will change back again.
EDIT - I just noted that you have Vista, the screenshots in the above are for windows 10 so it will look slightly different in Vista but it's the asme process.