Um. You...really shouldn't go choosing random graphics drivers. Mandriva automatically detects and uses the right driver for your card.
Hit ctrl-alt-f1 and you can log in to a console (log in as root). You can run drak3d and drakx11 in text mode. Run drakx11 and re-configure your card using the default (auto-detected) settings, then run drak3d and disable the 3D desktop. Then run 'service dm stop', wait five seconds, and run 'service dm start', and your desktop should come up. Then you can try enabling Compiz again, if you like, but don't go fiddling around with the graphics driver setting for no good reason. :)