I found this power requirements calculator. http://www.jscustompcs.com/power_supply/ From your description, I calculate about 330 Watts. (assuming a 9800 pro ~ XT). A 450 W should in theory be okay but that doesn't necessarily mean that it really outputs 450 w because manufacturers tend to mislead about their true power output, which is sometimes a lot lower. I'm not saying that is your problem, just something to think about.