You may recall that I recently purchased a dual 2.0GHz G5 system (this is the mid-2004 M9455LL/A - PowerMac7,3 - A1047 - 1969C model). It worked for the first day I had it then, after powering it off and coming back to use it the next day, it failed to boot. Problem symptoms were a power light which illuminated, then flashed bright three times, then the sequence repeated. No chime, no video, nothing but the flashing power light. Attempts to revive the system by removing unnecessary parts (really just memory as there was nothing else installed), an SMC reset, PRAM reset was out (requires the system to at least start), and replacing the battery (with a brand new one purchased months earlier) all failed. Searching online I came across the "About the Power Mac G5 (Late 2005) diagnostic LEDs" document which stated the power light flashing three times meant there was incompatible memory installed. I thought this odd because the system worked the day before with the exact memory it was now indicating was incompatible. I tried swapping the memory with another, functioning, G5 and the result was the same...power light flashing three times. The memory from the failed system worked fine in the functioning G5. Obviously memory was not the issue. Then I stumbled across an explanation which ended up being the problem: A failed motherboard. Apparently there is a problem with the G5 motherboard whereas some PGA chip, on the topside of the motherboard (hidden as it faces down and you cannot see it without removing the motherboard), for which the solder joints fail. This chip is right next to the processors and between the memory slots (again you cannot see the chip itself, just the square area where the chip is mounted from the other side). I was able to confirm this was the problem as I applied pressure to the affected area and the Mac began to boot until I released pressure at which time the failure symptoms returned. Unfortunately a motherboard replacement is beyond what this system is worth. So I decided to try reflowing the solder connections. Some people have pulled the motherboard and put it in an oven. Being the lazy guy I am I felt this was too much effort for the system. Instead I opted to try using a heat gun to selectively apply heat to the affected area. My first attempt at doing this failed...I think I was a little too conservative in heat application. I decided to give it a second go and apply more heat and for a longer time. I figured at this point what did I have to lose? I set the heat gun on the lowest setting (around 500 degrees) and held it about an inch from the affected area. I used a circular motion and applied the heat for about 15 minutes. The board was nice and toasty to the touch and I figured I would either not get it hot enough (i.e. the reflow would fail) or I would get it too hot and possibly damage something. The end result being the system would still be non-functional. Well, I'm happy to report that it worked and, after a cooling down period, the system powered on and I heard the familiar POST chime. I assembled the remaining parts, hooked it up to keyboard, mouse, and monitor and I am happily typing this response on the system. The question now becomes: Will it continue to function? I'm going to play with it over the next week or so to see but it's starting off on a positive note. The only issue is the cooling fans speeding up and slowing down (same behavior as I reported with my dual 2.7GHz system so I'll try the recommendations provided for that on this system). I'd post a photo of the affected area but it doesn't look like I can upload them to the site...has to be a URL.