iMac G5 startup disk woes :(

Have you checked to see that the caps are ok, not swollen or leaking? It could be that th logic board is failing, and the bad caps would contribute to this.

If you can boot in Target Disk Mode try running Disk Utility to see what's going on. If that doesn't show anythng, use the Apple Hardware Test disc, which came with your computer.

1. Insert the Mac OS X Install disc that came with your computer, then restart the computer while holding the C key.

2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)

Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.

3. Click the First Aid tab.

4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.

5. Select your Mac OS X volume.

6. Click Repair. Disk Utility checks and repairs the disk.

Caps are capacitors, those things that look like little soda cans. They are on the logic board and inside the power supply unit. If they're either swollen or leaking, they con compromise your machine. Here's a picture.

I'm going to give you my own tale of woe. My G5 iMac died after a power cut (totally dead - nothing at all). The repairers replaced the power supply and also put in a bigger HD (I needed one anyway).

After a few days with everything running fine, I began to get issues like yours. Bootup and login problems. Eventually I was running continuously in Safe Mode and not putting it to sleep overnight. Then I began to get problems like saving or pasting - I tried a Restart but it wouldn't log me back in. However, I could run Tiger on an eHD for a while, but then the FireWire ports went too, so I was stuffed.

It turned out to be the logic board. I bought a recon machine - same spec - on eBay, installed my new HD in that, and I was up and running again. So far (touch wood) it's ok. I think that's your issue. There's something amiss with the logic board. How far you want, or can, go down the path of getting a replacement is of course up to you.

Yes, it's amazing what difference a graphics card can make. I have a little HP netbook (very recent) running Windows 7 - the G5 still has it licked in most departments, but the HP runs video much smoother. I guess its low grade Intel integrated GFX chip still smacks the bottom of a state-of-the-art (for 2006) ATI Radeon X600 Pro.

The caps are indeed gone, swollen and leaking! Nasty! Replacing the logic board is not inexpensive, you are probably, best off by selling it for parts.

G5’s were wonderful machines, unfortunately I have the feeling yours is too ill for a reasonable action to repair it. Some luck if you find a similar product, and take the logic board from that one. Otheerwise MGW is of course right, sell it for parts, which is the reverse sense of action.😟

Give a try, G5s are wonderful machines, I still have a 12 in PowerBook for older apps, including classics. If not expensive, it is indeed worth trying.

Sorry, selling it is your best bet.... logic boards are expensive and yours is quite clearly dead (particularly since you don't want solder it).