Fix Apple Logo Keeps Running and Froze on Mac

If you had problem like this, I'd recommend you reset the PRAM (command + option + p + r at startup until you hear the startup chime again) and perhaps the PMU just to be thorough (remove battery, unplug it, hold down the power button for 5 seconds or so). Out of curiosity, what computer did you use to reinstall via target disk? If it was by any chance PPC, you didn't install the right one. Of course, you might just have a logic board problem, but if so, there's not much to do about it. Almost sounds like a potential system failure.

If you are unable to restart on a CD and can see the hard drive in Target Disk Mode, then hardware failure is a virtual certainty. You've really done all you can -- Apple will need to look at this Mac.