Hanging on blue screen during boot (but Safe Mode OK)

Question

Strange stuff with my iMac G5 -- machine boots normally, gets through Apple icon and spinning spiral, then hangs on blue screen and stays there. Mouse cursor moves but that's it.
Safe boot works normally, all safe-mode functions good. But need network, other services back.
History: Spent most of past week downloading huge, multi-gig file. It eventually downloaded successfully, but during process my wife put computer to sleep a couple of nights without halting download.
Didn't have adverse effect first time, but it froze Finder second and third times, necessitating reboots. Also killed wireless connections for all PCs in network those two times iMac needed reboot, had to reboot gateway as well.
Morning after download finished (Friday), iMac failed to wake up from sleep, wouldn't boot normally, had to go into Safe mode.
Additional RAM was recently installed, but has worked well. Safe mode shows full two gigs in use.
Solutions I've tried, without success:
-- Trashing network preferences in both user and system
-- Re-installing Finder and NetworkInterface apps using Pacifist
-- Removing recently installed extensions in System (extensions put back after that failed to resolve issue)
-- Removing recently installed Startup items (again, put back after that failed to resolve issue)
Clearly it's got something to do with the network interface, but I've tried everything I know how to do. Any ideas? I'm out of them.
Thanks in advance.

Answer 1

The Airport card is not removable in this model -- 2nd rev G5 iMac, with automatic light sensor.
But -- I think I've found what's wrong. Unfortunately there's no easy fix ...
It's most likely the bad-capacitor issue that plagued the 1st rev of G5 iMacs. (This particular machine was a refurb bought direct from Apple in the fall of 2005, so it's possible bad caps were put on during the refurbishing.)
I first heard about the problem a couple of days ago but figured a hardware diagnostic test would catch it. More online research reveals that the hardware test doesn't.
When I popped the case this morning to yank the new RAM, there were definitely a few capacitors that had domed tops. Nothing spilling out anywhere, which was what I was looking for, but I've since found out that even contained bulging is a sign of failure. The capacitors should be instead perfectly flat-topped.
So ... I'm gonna call Apple tomorrow morning and see how much it would cost to replace the mobo. There have been reports in forums that Apple sometimes offers to do it for free, even in cases occurring within the few months.
See this link for examples of Apple picking up the tab for complete mobo replacement: http://www.macosxhints.com/article.php?story=20090314071508354
If that offer isn't made, I will look into having the capacitors replaced. This is at the edge of my own technical abilities so I will first ask my techie friends if they can do it for $100 or so, plus parts ... and if not I'm gonna try to do it myself.
This guy shows you how and sells inexpensive parts to do it with: http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php
There is also a guy out in Missouri who replaces bad capacitors on motherboards for a living: http://www.badcaps.net/ Looks as if he'll charge between $80-120 including shipping and parts. So I may go that route.
In any case it turns out Apple did know about this issue back in 2005 and even instituted a program to fix iMacs that had problems stemming from it for free. (Dell Optiplex machines also had the same problem, which was traced back to a few Taiwanese manufacturers.)
Unfortunately there was no recall (Apple would never have lived that down) nor was the issue highly publicized. You had to wait until your own machine acted up, and then the free-repair program expired at the end of 2008.
I myself never knew about it until a few days ago, and I usually keep up on this stuff -- which is something I will make very clear when I'm on the phone with Apple tomorrow.