Crysis 2 and Windows 8.1

I've just tried upgrading to Windows 8.1 as a duel boot option and thought I'd give Crysis 2 a burst. At first I was pleasently surprised at the framerate increase which jumped from 60 fps in Windows 7 to 100 fps in Windows 8.1. Then, while playing the Sudden Impact level, I found I can't jump out of the window, which is under where the alien vessel crashed, which is the only way to move on to the next stage of the game. I uninstalled it and then reinstalled the game using the compatability option for Windows 7, then did the same for running the game, but no luck. I still can't climb out the damn window and move on with the game. Any help here would be very much appreciated, because I love all the Crytek games. Especially Crysis 2 and 3 and wouldn't mind staying with Windows 8.1 rather than dumping it.

Crysis 2 and Windows 8.1