I transfer the game file to my other computer (with the 5770), played it and found no flicker. I want to see if it is indeed the game issue or some sort of incompatibility with my current system. That's why I want to plug in the 5770 and see if the flicker still persist. I just don't know how to change the default to 5770, without having to uninstall the 7950. Basically I want to just plug in the 5770 without having to remove the 7950 and make the computer use the 5770.