The video card may be overheating. How warm does the ambient air inside your computer chassis get during operation? Also, if you touch the heatsync on the video card (just the metail heatsync, don't touch anything else), is it hot enough to cause pain? And if it's barely even warm, it could be that the heatsync is failing to do its job properly by not making good contact with the graphics processor. Another possiblity is that your power supply unit is not up to the task. What brand/model PSU does your system have? Thanks, -AT