Men of war demo performance issue

[Pharoah246]

Ok so I just downloaded the MoW demo about 2 days ago. After I had it all unzipped and installed I fired it up. Once I was on the main menu I checked the graphic settings it had on and everything was on high. So I ran through the singeplayer mission it gives you and It ran extremely smooth with a high frame rate. After I finished it I exited out of it back to the menu and turned off my computer for the day. The next day I fired it up again to play it again, but once I was in the mission it was lagging like hell. So I went back to the menu and lowered the graphics a bit but it was still lagging like hell with about 5 frames a second... I tried everything and nothing seemed to work. My Computer meets all the requirements for this game and is able to run it on high with most to all of the options maxed out. What basically happened was the very first time I played it it ran smooth with everything on high, and then from then on it was lagging with horrible performance.Any help would be greatly appreciated.

Thanks