i have osx and played nexius for 1 day and it turned black with colored crestals every whare help

You mean like red, green, blue dots and stuff? If so, it sounds like a graphic card error, something like overheating or something.
I'd suggest you post in the "Support/Bugs" category for more replies and more help. Unless someone can move this thread over there.

Does any other games give you these results too? And finally, what's the specifications for your computer? Drivers, memory, speed etc.?

In the nexuiz menu settings and video, be sure texture compression is set to none.