iMac12,2 wont start after the last SU. HT starts but loops. Start from CD seems also broken/irregular

Hi !

I made the last SU for 2 or 3 days and I worked also a while. When I go for a longer pause I started the screensaver.

When I was back I found the screensaver freezed and no option to wake it (sometimes I had with another Mac screensaver freezes that I solved with putting in sleep with the power button and waking after a lot o seconds).

After the usual force to go off and restarting on singleuser i cannot execute a regular fsck -fy or an applejack AUTO restart because the first command seems not to work and the applejack.sh was not found.

Than I tried to start with the Installer DVD (first 2/3 times without success) and also with the Hardwaretest (HT) DVD.

The HT comes to start but loops/freezes after the 1 Step (Checking the System) before the Test begins.

I have also made a reset of PowerManagement with command+option+p+r

Now I want to connect per FireWire the iMac to my G5 but I see not only the FW Symbol on the monitor but also a (?) Power Symbol (a grayed Circle with a flash) and the iMac do not appears on the Desktop as a "slaved" FW Disk

Is this Problem known?

How to workaround?

Every help is welcome

Massimo