RAM must be installed in opposing pairs, but no LEDs sounds bad.
Might be time to replace the PRAM Battery, 4 years is close to their lifespan, far less if ever without AC power, & can cause strange startup problems...
See which one your G5 has...
I tried changing the battery with no luck. I did fumble around for a bit and now the mac sounds starts up with the mac. That started after i took the GT 6600 out and put it back in. Also i have an all aluminum Cinema Display plugged in not the one with the Face-time Camera but while the Cinema Display is plugged into the mac its LED. When its plugged into my PC how ever the LED stays on which it always has done. So It knows its plugged into a Mac but still nothing shows up on the Cinema Display or my 2nd LG monitor that is also plugged in. When I press the power button to shut off the Mac the 7 diagnostic LED lights up then the mac powers off which is the same as the one that lights up for a second when you power the mac on. Is that normal for that LED to go red when i power it off too or is that part of the problem?
the power LED went crazy flashing...
Can you count the beeps or flashes?
1 beep = no RAM installed
2 beeps = incompatible RAM types
3 beeps = no good banks
4 beeps = no good boot images in the boot ROM (and/or bad sys config block)
5 beeps = processor is not usable
In addition to the beeps, on some computers the power LED will flash a corresponding number of times plus one. The LED will repeat the sequence after approximately a 5-second pause. The tones are only played once.
Note: In this case, a flash is considered to be 1/4 second or 250 ms or greater in length.
If one of the Apple LCD displays detects an error condition, the power LED will flash in a certain pattern to indicate the issue.
short, short, short
The display is detecting wrong video format or an unsupported resolution.
Verify that your equipment is compatible and restart the computer. If the issue continues, reset the PRAM.
short, long, short
Make sure you are using the correct power adapter with the display. This alert will only appear on displays built in 2004 or later which require an external power adapter.
short, short, long
The display is detecting a backlight error. Check your display's power connections and restart the computer. If the problem continues, contact Apple or an Apple Authorized Service Provider.
The cinema Display's LED just stays off and the G5's stays solid unless i hold the power button till it beeps and then the G5's LED flashes like crazy till the Mac sound plays. I did the same thing on my 2007 IMac and it does the same thing it beeps then the mac sound plays when you hold the power button. I guess when you do that your resetting the SMC. The Power Mac seams fine other then i just cant get any display from the GT 6600. I tried another GT 6600 from another G5 i have that has the same problem as this one and both cant seam to pull a display i tried other monitors too. I even put in a GT 120 and a HD 5570 just to see if they would do anything but nope i cant seem to get a display on both G5s with any graphics cards or monitors.
I even put in a GT 120 and a HD 5570 just to see if they would do anything
Those are Intel Mac only.
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...
Heat gun better...