I've got a 6-year old iMac G5 that has served me well. Yesterday, it flipped out, giving me some weird colors before ceasing operations. When I re-booted, it gave me some old colors, turned the power light off and just hung on a grey screen. I followed the excellent Apple instructions here - http://support.apple.com/kb/ht2173 - and I've found that it boots just fine from the internal power button. But when I put the cover back on and try the external power, no dice. A few years ago, the Genius Bar did some sort of recall/electrical fix on it. A blown capacitor, I think. Any ideas why this is happening? And what, short of buying a new iMac, can be done to fix it?