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Since it started up once, it sounds more like a fried power supply in this particular case, but there is a section over at MacInTouch that popped up right after that big blackout hulabaloo on the East Coast a while back that has suggestions for resurrecting computers with symptoms similar to yours.

I mention this because at one point a friend's Quicksilver died on him in a similar fashion, and I managed to resurrect it without replacing anything. What I tried:

Unplug it. Pull the motherboard battery (you've already put a new one in, which is a good thought). Push the power button on the front to drain any residual charge (it usually lights briefly and the fans'll twich). Push the motherboard reset button just for good measure, and you can even let it sit in this state for a while, to be sure everything is really dead. Then, re-plug, re-insert battery, and push the motherboard button briefly, once only. See if it starts up while holding down command-option-o-f, and if so do a reset-nvram and reset-all. Some Macintouch folks recommended leaving it unplugged for a full 24 hours, but that wasn't necessary for the one I fixed.

In your case you've done pretty much everything in this dance, and it still didn't work, so it's probably the PSU (at least, if you're lucky that's all that's wrong).
 
None of the above has worked. I pronounce the Quicksilver DOA.

I may take one more step. I may take it in to the local repair shop for a $50 min. charge diagnosis. It may be worth that just to find out if it can be brought back to life for a reasonable fee.

Otherwise, selling it off in pieces on eBay is looking more like the thing to do.

Thanks for for the words of advice from everyone and for the humor too.
 
mistermr said:
None of the above has worked. I pronounce the Quicksilver DOA.

I may take one more step. I may take it in to the local repair shop for a $50 min. charge diagnosis. It may be worth that just to find out if it can be brought back to life for a reasonable fee.

Otherwise, selling it off in pieces on eBay is looking more like the thing to do.

Thanks for for the words of advice from everyone and for the humor too.
Have you tried another power supply in it?
 
I don't currently have another power supply to put in it. None of the dozen or so other Macs I have here share the same power supply.

It is now in the shop. For $47.50 they will either tell me what it is or that they couldn't find the problem within the minimum half hour of diagnostic time.

If they find what it is and the cost is reasonable, I'll have it fixed or do it myself. Even if they don't ID the problem I should still get more than $52.50 out of it for parts but the diagnostic charge is still worth it if I can find out what can be sold as working. I'm hoping for a best case scenario where it's a cheap fix but I'll plan for the worst too. Gotta be realistic.
 
If you end up spending like $300 its still worth it. Its like buying a used computer for $300.

You spent $5 on it!!! Of course it would need repairs...
 
mistermr said:
I don't currently have another power supply to put in it. None of the dozen or so other Macs I have here share the same power supply.

It is now in the shop. For $47.50 they will either tell me what it is or that they couldn't find the problem within the minimum half hour of diagnostic time.

If they find what it is and the cost is reasonable, I'll have it fixed or do it myself. Even if they don't ID the problem I should still get more than $52.50 out of it for parts but the diagnostic charge is still worth it if I can find out what can be sold as working. I'm hoping for a best case scenario where it's a cheap fix but I'll plan for the worst too. Gotta be realistic.
If they can't fix it, I will absolutely, seriously, give you $70 plus shipping for it.
 
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