First question is what's your OS. I suspect its Windows 7 cos it's a familiar sounding woe as a guy who came from XP and under 7 games get installed into weird places.
One of the suggestions I've come across just from googling issues is to simply reinstall (as in uninstall and reinstall) the game and patch. It's a pain but sometimes works as a fix.
Another fixt talks about a situation depending on whether its a steam download - rather than cut and paste I'll just include the link
it's just from the steam forums.
As for a time when you just installed the game and it ran....that's always actually been a rarity. What's really changed is the degree of unfinished state that new games are allowed to get away with, sometimes the initial patches are larger than previous years entire games and you're expected to download these fixes at your cost. Seems that progress means prettier games with shoddier code.