hard drive won’t read

Well I have this compaq 1G computer in the tech shop right now and it won’t read an image because the hard drive won’t kick. Ihave replaced it and still no joy. I am either thinking that it could be the motherboard, maybe the cmos battery or the power supply. Iwas just wondering if anyone has run into this problem before and if you could get back to me if you have any suggestions.
Thanks Melissa