Fist of all, give the exact specs of your machine, i.e. mobo, amount of ram, ect.
Second, you decribe your problem to vaguely. Does this happen when you boot of the mandrake cd's , or after you installed it and boot up for the fist time?
Don't want to cause panic or somthing, but this could be an hardware fault. Check if your ram is okey. You can do this by downloading "memtest" . You can download it here