The iMac's Role In My Determination To Drive Myself Mad. (Updated)

A long, long time ago I bought a shiny new iMac G3 computer.
I remember how Linda and I giggled as we ran through the shopping centre in Croydon with the box swinging wildly between us.
Over the years, before it's replacement, I sat in front of it at every available opportunity.
Eventually I replaced it with a shiny G5 iMac and it went to live in the attic with the rest of the out-of-date forgotten possessions.

About a year ago I dug it out again and tried to restart it.
Unsurprisingly it failed to spark into life even though it's power indicator lit up and things inside it whirred.
I put it back in the attic and forgot about it again.

Fast forward to January this year...
Linda arrives home with an old G3 iMac her employers were throwing out.
I, attempting to be clever, decided to re-install the O/S to clear it's memory of anything left from it's previous life.
The C.D. drive had become sticky and, half-way through the install, refused to eject the installation discs.
I put it in the attic and forgot about it.

This morning I decided it was time to get rid of all the useless dead computers that had accumulated in the attic but thought I'd have one last go at getting the most recent addition to the heap working again.

The first successful operation was getting the trapped install disc out of the drive and the managing to re-install the whole O/S, loosening up the disc-drive in the process.
After 2 hours I have a working 600 mHz G3 iMac loaded with O/S 10.1.2:

 I installed my old version of Reason on it, the one I couldn't use after I'd installed Lion on my laptop, bonus!
Linda tells me it now works faster than it ever did at her work-place, double bonus!
Beyond using it as an electronic music work-station I can't think of anything else to do with it at the moment.

Flushed with success I decided to have one last go at reviving my original G3.
On booting, inserting an O/S 9 installation disc and restarting, I find it's actually installing!
An hour goes by and I have another working G3:

One of the problems it used to have was an unstable video display but now the screen's as steady as a rock.
So, I decide to update it to O/S 10, just like the other one.
Another hour passes and the installation is complete but the unstable display has returned.

Bum.

On searching the geeky end of the interweb I'm now under the impression I should have done a firmware update before installing O/S 10.

I think I'll turn it into a fish tank instead.

Update:


After tippy-tapping this post I connected the blue G3 to the interweb hoping that updating the O/S might cure the screen problem.
Switching the machine on, I find it's cured itself and my joy returns.
After about an hour the screen starts to deteriorate again.
I think something may be dying, inside both the G3 and me.

On a lighter note..
The 'rescued' G3 is fine and I've put a request out on Freegle for a copy of O/S 10.3 'Panther' to install on it.