'I was having a problem with several ports that did not work.' - first, help the rest of us understand what you mean by this. Typically, when one states 'ports' on the internet, they mean
TCP/IP ports. If you mean anything otherwise, you must state such explicitly.
Since I will assume 'ports' means TPC/IP ports then ''I used the techtool pro disk ... did not offer to repair anything.' is meaningless.
'... Please help', OK, now regardless of the material presented - if you need to repair the iMac G5's hard disk drive (regardless of the number of partitions), boot from the 'Tiger' installation DVD or the 'other' bootale partition and run 'Disk Utility' from it. Next, select the original boot partition and then click on the 'Repair Disk' button under the 'First Aid' tab. No 'Techtool Pro', no 'Disk Warrior' - nothing; only, 'Disk Utility'.
What baffles me is 'I reinstalled the system on a different partition but the old boot partition is still unmountable.'. Why?, because the iMac G5 is sold (by Apple) with a single partition, and with the latest MacOS X version installed; and, by default (via 'Disk Utility', DU) one cannot create additional partitions without wiping out any existing partitions - plus, DU will not allow one to erase / partition the current boot drive.
Also, if a volume or partition is 'unmountable' that is because an application / process on it is in use.
Never, mentioned was that the iMac G5 was booted from the 'other' partition.
If mulitple partitions (somehow) did exist, prior to the MacOS X installation on the 'other' partition; thus, as already explained above - boot from the 'Tiger' installation DVD or the 'other' bootable partition - run it's copy of 'Disk Utility' and attempt to to repair the 'original' boot partition.
If 'Disk Utility' reports unrepairable hard drive problems - then bite the MacOS X bullet and reinstall MacOS X on the original partition ('Erase and Install', or equivalent, via the installation processes 'Options' buttons), all related updates, etc.