iMac G5 iSight - help needed with hard drive issue

Hi, I'm now very close to taking a hammer to my G5 iSight so desperate for any advice. The hard drive and PSU were faulty and both have now been replaced. The superdrive also only boots from CDs not DVDs so I was heading down the Ubuntu route to at least get an OS on it (only have Tiger or Leopard on retail DVDs). I can boot into open firmware and boot off ubuntu on a USB stick but the installer and GPARTED cannot see the hard disk. I know this hd is fine as have tested it on a PC, created and deleted partitions and volumes no problem, and have also tested the SATA cable in the iMac. using open firmware, it looks like it thinks there is a disk there on the sata controller (using dev / ls and devalias). I've also tried reset PRAM and SMU but no good. other than that, iMAc seems OK - ie can boot to Ubuntu from the USB stick, but when run the partition editor it cant see the internal hard disk at all. I've also had the logic board out and checked all capacitors for signs of leakage etc and anything else that might cause an issue. Now come to a dead end. Anyone got any ideas of what I could try next?

 

thanks very much for your advice. It was that! Now have managed to get Leopard installed so looking good apart from the fact that it is overheating now. suspect I may have dislodged some of the connectors on the logic board and not replaced them properly. Particularly the one big one just below the Superdrive ribbon connector. Couple of the pins are loose. Would you happen to know what this connector controls and what the pin outs are for it?