Hi Ken, very likely he Video card, but need specific nfo on the Mac for video card recommendations.
Foes it safe boot?
One way to test is to Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, Test for problem in Safe Mode...
PS. Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive
Reboot, test again.
If it only does it in Regular Boot, then it could be some hardware problem like Video card, (Quartz is turned off in Safe Mode), or Airport, or some USB or Firewire device, or 3rd party add-on, Check System Preferences>Accounts>Login Items window to see if it or something relevant is listed.
Check the System Preferences>Other Row, for 3rd party Pref Panes.
Finally was able to replicate the problem.
Here's what I have found.
- If the computer stays off for a week or so, it will not start up with video unless left running for several hours, then manually restarted.
- If the computer starts up normally, putting it to sleep for about 45 min will cause the green blocks to appear.
- When the computer is restarted right away after the green blocks, the video does not come up, but connecting with screen sharing shows this in system profiler:
Attempting to start into safe mode produces no different results, still no video.
There are no 3rd party pref panes installed, and this occurs with no peripherals except keyboard and mouse connected.
About this Mac:
Model Name: Power Mac G5
Model Identifier: PowerMac7,2
Processor Name: PowerPC 970 (2.2)
Processor Speed: 1.6 GHz
Number Of CPUs: 1
L2 Cache (per CPU): 512 KB
Memory: 2.25 GB
Bus Speed: 800 MHz
Boot ROM Version: 5.1.5f2
Where your sure it's not the monitor. With the green screen is a indication of video card or driver. I'd first work with the driver, re-install or update the driver. Unless you have a video card to swap out. I've only seen a video card go bad once in 10 years but it could very well be the card, but nearly every time it's been the driver.
How would I go about reinstalling the driver?
You can't. These aren't Windows boxes.
Drivers are a part of OS X. Only an occasional retail Radeon card has stand alone drivers, but those are always included in later versions of an OS.
If you need drivers, update OS X with a combo update; example 10.4.11 or 10.5.8.
However, drivers aren't your issue.
Graphics card failures are not uncommon, Mac or PC, and present as you describe, among other ways.
A card without a proper ROM or driver should still have a vendor ID report in Hardware/Graphics.
This I have seen with all Mac or PC cards (prior to flashing) in OS X.