Did you switch the logic boards? They are assigned to the PS3 motherboards, so if you put your drive in without switching the logic board that is why. If not then you are having the exact same problem as me, except I'm pretty sure mines a broken ribbon.
I'm not sure if thats nooby enough..I mean no offence to you of course, just incase you don't know I'll save you having to ask another question :P
The logic board is the small PCB board that is screwed onto the BluRay drive
Yes, I am a noob, but I am not stupid.
System progress: 60GB 3.55 KMEAW installed, YLOD fixed, working replacement BluRay Drive..will have ribbon tomorrow, so hopefully my system will be up and running!
Big up to Pereb27