Sula

My apologies if I'm in the wrong forum. This is my first post. Bought Arma 2 and Arrowhead via a Steam download two days ago, and was amazed to find buying via download works! Started training as a recruit in Arma 2 but after I use the firing range I find often the screen freezes and then I get kicked back to my desktop but the game thumbnail is still open on my toolbar. Also, the Steam news box pops up. Is this likely to be something to do with my hardware/software (I'm thinking anything from drivers to graphics card?) or might it be related to the steam pop up news box that appears after I exit the game normally or when the game kicks me back to desktop? Or maybe I'm in the wrong forum and this is a well known bug? I'd appreciate any advice and help anyone is kind enough to offer. Many thanks, Sula