|So your computer will not boot up?|
It may not be connected to the Master/Slave settings at all. But if you do want to change these you need to actually get inside the computer and look at the back of the hard disk and the CD-Rom drive.
Both will look similar to this: http://www.recovery-soft.com/resource/images/install-ide-hard-drive3.jpg.
On the photo I've linked to there is a white, plastic rectangle around some of the pins. It's called a "Jumper" and it sets whether a drive is master/slave. You need to look at the instructions that SHOULD be stuck to the hard-disk and put the jumper in the correct place so the hard disk is set to "Master".
Whether that will fix your boot-up problems I don't know.