Did you try Right click and select "Open With" and then choose from the
application list i.e. a web browser.....
I don't know why it wouldn't open; I would have assumed that the file
association *.html would by default, open with your web browser.
But I would scan for viruses/spyware etc first - sounds like a suspicious
file to me because HTML files are not applications. They are merely text
files which display in a web browser.