If it has only been freezing since you added the hardware yu can bet your bottom ddollar it's that which is causing the problem - and my money would be on the graphics card...you also need to ensure any drivers / software required is the EXACT version!
If it is memory - the amount of beeps you get on start up should differ. Try removing the graphics card and its software and see if the problem still occurs. If not, put it back and try removing the memory.
If neither of these sorts it, you then need to disable everything but the essentuial files at start-up using msconfig and restart - if that works, add one back and restart again until one of the proceesses running at start-up is causing the hang.