Unique Not powering On Issue?

Good day!

I recently bought an old G5 Powermac Dual 2.0Ghz along with a 23" Cinema Display. Model is an A1047, EMC 1969, PowerMac 7,2, made June 2003-June 2004; all based on the Serial lookup on everymac:

https://everymac.com/systems/apple/power...

Aftermarket ad-ons, which were already installed:

• There is an aftermarket ATI Radeon 9800Pro 256mb Graphics Card installed. The GPU fan does spin.

• There is 1.5GB of RAM (6x256MB).

• It did NOT come with a hard drive, but I do have 2 working hard drives which I installed to see if I could get it to boot. One with 10.5, and one with 10.0 (although, I realize that everymac says 10.2 is the lowest it came with).

I have done research and haven't been able to find anything based on my specific problem(s):

• First, and this is the weirdest based on not being able to find anything about it….when power it on the LED light turned on as the button is press; however, as soon as I remove my finger the LED turns off - yet the machine is still running. Anytime after removing my finger from the power button (meaning that the LED is off while the machine is on) if I press the button the light will turn on, and as soon as I remove my finger from the button the LED power light turns right back off (but not the machine).

• There is NO chime.

• The fans ARE running.

• If I leave it running for about 1-2 mins the funs begin to spin very fast…it sounds like an aircraft! lol

• There is NO display to the, Cinema display, which DOES work as tested through the ADC to DVI adapter to my other Mac.

• Various, and working, USB keyboards and mice do not work. Caps lock will not light up, and the mice have no optical lighting underneath. Also, the eject button on the keyboard doesn't do anything.

What I have tried, based on other articles:

• Power supply does click when plugged in, read in the Apple manual that good ones often do that.
• Swapping the positions of the CPUs.
• Running only 1 CPU on the #1 (top) CPU slot; tried with both CPUs.
• Reseating the RAM.
• Using different combinations of the RAM (however using the same amounts, same locations on both sides).
• Removing the graphics card to see if the boot up chime will happen (read that can be a way to test if it is bad, when you don’t have an extra GC laying around).
• I was able to use a paperclip to open the DVD drive, and it does closed by itself when you push the tray.
• Replaced the PRAM battery.
• Tried resetting the SMU by pressing the SMU reset button on the logic board.
• Ensured the CPUs were seated correctly.
• Capacitors look good

Note, that in all of the various combinations mentioned, the power LED light does not stay on unless the power button itself is being pressed.

What are some of your thoughts here? I feel that testing the logic board and individual CPUs with ones known to work would be the next best approach; however, before going out and buying anything I thought I would see what others thought!

Hopefully, this can help someone else too!

Thank you for any help you may provide! :)