It turned out that there are serious problems with the HDD.
So I tried to fix it by using one of the HDD "cleaning" programs from "Ultimate Boot Disk".
Started well, but turned out questionable...

I've actually never used this program before, so I'm not totally sure what's meant by all those "drive not ready" errors.
Is it possible that all the NRDY sectors are bad sectors?
If that's the fact, I assume the old HDD is dead

Or can anyone of you give me some hope or ideas, how to reanimate it?