Besides your bios settings,you need check your harddisk and cd-rom jumper settings.It is not a fixed rules to connect those IDE devices.But you must remember 1 master with 1 slave.It doesn't set the jumper to "cable select".It can cause more unstable status.If you ask me how to detect the hd & dvd-rom.The harddisk connect the ide0,the dvd-rom with cd-rom connect on ide1.(advice,it can get better system performance).