I was recently given an iMac (24-inch Early 2008) without a hard drive. Following the instructions on iFixit, I gave the computer a hard drive, installed Mavericks on it, and didn't notice anything damaged/broken.
The computer worked really well a few times, then began not starting up properly.
Disk Utility didn't report anything wrong.
Nevertheless, it would either start properly, then work for a while and shut down (or not), stay stuck on the startup chime, the screen would remain blank at startup, or display typical kernel panic messages such as:
I reset SRC, same problem. When trying to start Apple Hardware Test (starting up with D key pressed), the screen would remain black and a sound would be heard "du-du-du-du-du" until I force it to shut down.
After finding articles about similar issues, I opened the RAM trap and removed the two 2GB bars of RAM that were inside:
Since then, when I try to start it up, the screen remains black and I hear a sound every second which is not the startup chime.