freeze in normal graphics Help

[1scorpio]

I am using Ubuntu 8.04 Hardy Heron With ATI catalyst graphics card in normal mode. when I change to extra mode the computer freezes. by that I mean Locks up and is completely unusable. I suspect that this is an openGL issue but I am not sure how to correct it. Any help will be appreciated.

TIA
1scorpio

[realgt]

please post specs on your machine to troubleshoot it further...need details on the video card if possible.