It sounds like the boot loader isn't configured properly... One quick way to fix your issue might be to boot into Mandrake, go into configure my computer and try using the auto-tools to set up grub. What might happen (and I've seen happen in the past, although not with 10) is that Mandrake will fix itself when reconfiguring the new boot loader.
Off-hand I'm not 100% sure of how to flip from lilo to grub though...
Also, you might want to consider a more accurate title. I tend to overlook posts where I can't see the specific issue just by reading the title