i ran glxgears and the 3 colored gears did appear if that helps

if you have the 3 D colored gears its mean that you have a 3d aceleration provided by default graphic drivers.

But the output of this command also give to yout the FPS result of your config an example->

302 frames in 5.0 seconds = 60.305 FPS
301 frames in 5.0 seconds = 60.014 FPS
301 frames in 5.0 seconds = 60.014 FPS
284 frames in 5.0 seconds = 56.626 FPS
301 frames in 5.0 seconds = 60.007 FPS
300 frames in 5.0 seconds = 59.977 FPS
301 frames in 5.0 seconds = 60.055 FPS
301 frames in 5.0 seconds = 59.931 FPS
300 frames in 5.0 seconds = 59.893 FPS


if you have a less FPS maybe your config cant run some games, or games work with slowly image.

If you can try launch games by terminal for example i have the game warzone2100 if i have a problem of closed GUI i open my terminal and put the command
warzone2100 if the image GUI close the terminal give to me any reason for this.

And finally i have some problems with xubuntu and Lubuntu with my older ATI (non-maintained proprietary driver for linux) Radeon 9250 PRO, i have a problem with games and 3d aceleration, the only solution for me to solve problem its very simple install mesa-utils.

You can find the solution i mentioned here->

http://ubuntuforums.org/showthread.php?t=2089840

I can solve that problem on my both pcs one desk and other laptop, in two i have same problem.

It can be possible that you have a similar problem like me.