Do you hear the boot tone (chime) as you power up?
Is the white LED steady or flashing above the power button, or is it off?
How old is your PRAM battery? If it hasn't been changed in a while, it probably could use it.
Have you tried a safe boot by holding down the shift key when you power up the machine?
Have you tried a PMU/SMU reset?
Finally, if you let it sit in the monitor-dark state for about ten minutes after powering, do the fans rev up to full speed?
This may indicate that the video card has tanked if the fans do not rev up.
jamesfromlos molinos wrote:
I do hear the chime, the white light is flashing, I don't think the PRAM has ever been changed, haven't started in safe mode, and the fans go to full speed after a few minutes. What is a PMU/SMU reset?
Is it flashing in a rhythmic pattern, as in, say two or three flashes, pause, same number of flashes about five seconds later and continuing?
A power-on self test in the computer’s ROM automatically runs whenever the computer is started up after being fully shut down (the test does not run if the computer is only restarted). If the test detects a problem, the status LED located above the power button on the front of the computer will flash in the following ways:
• 2 Flashes: No RAM is installed or detected.
• 3 Flashes: Incompatible RAM types are installed.
• 4 Flashes: No RAM banks passed memory testing.
One thing to try if any of the three items is true is to reseat the memory DIMMs (remove from the logic board and then reinstall). If the number of flashes is greater than four, though, then you have serious problems beyond the memory.
If you're sure the RAM is good, try the Hair Dryer trick...
No power light at all...
It can show on any G5, and even many other computers & electronic devices of the period.
And see this last one in particular...