imac G5 will not boot, makes fan noise
My G5 from 2006 running OS 10.5 was on and working fine this morning. I went out for one hour, when I came back the display was dark, and the fan was running at mega speed. Much louder and faster than ever. I had to unplug to get it to turn off. The computer will now not boot, or will partially boot, showing the desktop sometimes, then freeze and the fan will rev up again. I've tried to use restore discs, boot from OS discs, boot from a cloned drive, nothing works. On one attempt, I saw purpleish lines across the screen (display?). I give up. I have no idea what to do now. I thought I could start up the computer and run it from a cloned disc in the event the hard drive is out. However, since i have seen the desktop on several boot attempts I think it is something else. Any advice before I go to a repair center for analysis?
Thanks.
iMac, Mac OS X (10.5.8), PPC G5 20"