iMac alu 20inch can't detected hdd

[Pineapple2111]

Hi I got an iMac 20" and suddenly it stops working when I switched it on the next morning, I put in my installation DVD, and disk utility doesn't recgonize it.
I opened it up and replaced a new 1tb hdd(iMacs out of warranty).
It still does not recgonize my new hdd.and shockingly my original iMac is still working when I installed it on an external 3.5 case.

Any ideas wats going on?

 

[koko32]

sounds like what happened to me. I think it is the power supply. I need to get my hd out. How did you open the back. See my thread from koko32. I describe the problem there. thanks