What games? I ask because you have a dual core CPU and not all games will run smooth on one. The resolution is low as well, but the GTX550TI doesn't have the power if you are maxing everything out (like everything up and 8xAA).
Lowest res they use is 1600x900. Its bigger then your 1024x768, but they probably use a faster CPU as well so depending on your system it might be close to what you get. The 550TI is not a monster gamer. It gets barely 30FPS in a game you mentioned. That's why I asked the questions I did in my first post. GTX550TI having problems? Not a big surprise if you are playing recent games at high settings.