It's probably the driver for your graphics card setting a graphics mode that either the graphics card or the monitor doesn't like.
There are a number of things you can do: pljvaldez suggests one option to force the driver to a compatibility mode, but that may not help if it's your monitor that's the problem.
There's some documentation here; see the very last paragraph in particular: http://wiki.mandriva.com/en/Docs/Ins..._does_not_work
You may be able to just select a vgalo or text install method from the menu. Alternatively, there may be an errata (http://wiki.mandriva.com/en/Releases/Mandriva/Errata
Another thing you could try is holding crtl+alt and pressing the + key on the numeric keypad, which usually switches between available graphics modes. This may let you find a mode that will work well enough to bring up a graphics configuration program.
Hope that helps,
— Robert J Lee