Have you checked for updates for your G-Force drivers?

Most times I've heard of that happening, it's been a driver clash or something similar. Generally video card related.

You could try adjusting the video card settings. Turn gaming or 3D acceleration off. With that brand of video card, I am aware such settings have affected online games also.

Edit: RAM did cross my mind. Glad you mentioned it Peerless. I have a bad ram chip on my machine. Bad RAM can also have same effect as you're having.