I wonder if your LiveCD is OK for a 64-bit environment? Does is say "64-bit" anywhere on the CD? If not then I am guessing it is 32-bit. On the other hand maybe a 32 bit LiveCD would not even get that far!
Next check is the nVidia graphics card: given your motherboard I am assuming this is pretty recent so it should be supported. However, what is it? nVidia support for older cards is sometimes an issue - it is usually possible, but can require some effort.
Finally, LiveCDs try to guess all the possible driver requirements and generally do very good job at it. However, maybe your setup is too exotic for Mandriva? I don't know, I'm a Gentoo man myself, but you could try other LiveCDs instead - they might have the necessary drivers.