I went through all the normal fixes. (Delete battle.net folder, make sure secondary login is enabled, etc.) nothing worked. Finally I copied the battle.net folder from a computer where the installer did work. This allowed me to at least bypass the updating setup files and install the game, but it appears this issue is still related to the running of Agent.exe as anytime I run the launcher, nothing happens. The game even seems as though it updates itself (though it goes through the same update process every time it is launched) but clicking Play does nothing, the launcher just hangs.
This seems like a pretty big issue with Agent.exe, many people having issues, the fixes offered do help some, but not everyone.
Edit: Window 7 x64