Looping/repeating problem with demo

[Veros]

I've been thinking about buying Defcon but when trying the demo from Steam I'm encountering an unusual problem. The game runs but various things constantly loop instead of playing out normally. The game seems to jump back several seconds to where it was beforehand when I'm not in the options menu.

As an example when I sometimes try to exit I'm unable to without using Alt+F4 as the purchase reminder screens timer resets. If I try to play a game or go through the tutorial I can't read messages as they restart before completely finishing and any commands or say targets for an icbm will be reset before taking effect.

To re-iterate, it's not that the game is stuttering but rather it's constantly repeating from the same fixed point and does not affect mouse movement, option menus, etc., only the in-game interface, messages and things like the title screens animated background (ie globe moves into view on title screen and starts turning as normal, then after five seconds it moves onto the screen again and starts turning as normal, keeps repeating as such).

My framerate is not affected at all nor is my sound, everything displays correctly at excellent speeds. When not running any software firewalls/anti-virus programs this still occurs. I've got my computer set up in my gateway's DMZ to avoid any port issues and I'm not running any other non-system processes that could affect it. Reducing the graphical or sound quality makes no difference.

My system specs follow:

OS - Windows XP Media Center Edition 2005
Processor - AMD Athlon 64 3200+ 2.4GHz
Motherboard - ASUS A8R32-MVP Deluxe
Memory - 2 GB of OCZ El Platinum DDR PC3200 in dual channel mode
Direct X Version - 9.0c
Video card - ASUS Radeon EAX550GE 256MB, Catalyst Driver Version 7.7
Sound card - Soundblaster Live!, Creative Driver Version 5.12.0001.0252

Any assistance as to what may be causing this or how to resolve it would be appreciated.