The first thing to do is to return it to as close to the original configuration as possible.
Next see what the diagnostics lights are telling you. Tearing into a machine without knowing what you are looking for is a very bad idea.
UPDATE 6/18/16
"Interpreting the LEDs"
"To interpret the LED indications, refer to the following table:"
"LED Indication On Off"
"1 Main logic board"
"detects trickle voltage from the power supply."
"iMac (24-inch) is con-"
"nected to a working AC power source. The LED will remain on even when the com- puter has been shut down or put to sleep."
"AC power source"
"is disconnected or power supply is faulty."
"2 Main logic board"
"detects proper power from the power supply when the computer is turned on."
"Computer is turned on"
"and power supply is working correctly."
"LED 2 will be off"
"when the computer is turned off or the power supply is working incorrectly."
"3 Communication exists"
"between computer and video card."
"Computer is communi-"
"cating properly with video card."
"If LEDs 1 and 2 are"
"on and you heard the startup sound, but LED 3 is off, video card may either be installed incorrectly or need replacement."
"4 Communication exists"
"between computer and LCD panel."
"Computer is turned on"
"and video signal"
"is being generated. If LED 4 is on and there is no display on panel, panel or"
"inverter may either be"
"installed incorrectly or need replacement."
"LED 4 will be off if"
"the computer is turned off or if no video signal is being generated."
"Front"
"Computer has power"
"but no video signal."
"Computer is starting"
"up or display has entered sleep mode, turning off the video signal."
"The front LED will"
"pulse when the entire system has entered Energy Saver mode."
3 Comments
mayer thanks for your interest maybe you're the only person who can help me, Mac is in its original state, no change of cpu or another, no flashing LEDs on the front panel, just turn it off after 1 second.
I bought this mac on ebay a few Euros just to use houses, the first time I turned it, the LED remains lit but no apple initial gong and no video signal, I spend and I turned back for the second time and has started well until the folder with question why but there was the operating system, then turned regularly and put in the box for a few days. Yesterday I wanted to install the operating system and has this problem, it turns off immediately, this is very strange, I do not think it's the power supply ....
by rbutry
nobody can help me for my problem?
by rbutry
UPGRADE
SOLVED
I downloaded a technical manual for this g5, I checked all the power supply voltages, and it was all ok. I changed the CPU and Mac is a good start, now it's all right, never the cpu although he had no obvious damage was damaged.
I hope that this solution can autrare someone else.
by rbutry