Try this:
http://www.bleepingcomputer.com/virus-removal/remove-coupondropdown
http://deletemalware.blogspot.com/2013/01/remove-coupondropdown-pop-ups-uninstall.html
It might hijack web browser shortcut as well, so use Shortcut cleaner:
http://www.bleepingcomputer.com/download/shortcut-cleaner/