WD Green Desktop HDD not booting

I have just tried to repalce a HDD on my home PC which is COMPAQ PRESARIO SR5249UK. I have selected the HD to boot from the CD drive with Windows 8 , Nada, nothing, just a message saying insert system disk. Anu ideas?

What size drive is the Green drive?

THe drive is 500GB

I have set the Boot sequence on the PC Boot to boot from CD to load a new OS Windows 8 the DVD spins but then nothing!!