I have an old iMac with picture problems. The problems started when I
opened the case to fix the CD-ROM, and I accidentally dropped a small
screw into the machine... I had to pick it up and carefully rotate it
to and fro so that the screw would fall out. I didn't shake the
machine, and I don't think the screw came into contact with the CRT
circuitry; but from the first time I turned it on afterwards, it's had
problems.

When I turn on the iMac, it'll start booting fine until it tries to
power up the display. At that point either of two things will happen:
it'll immediately cut power and the whole machine will go dead; or else
the video will appear as a bright green, and otherwise the Mac will
work properly. When the video is green, I mean a bright lime green with
no other tints to it, and the desktop is shifted way to the left so
that part of the image is off-screen (though the unused right side of
the screen is bright green as well), but the cursor, icons, etc. are
visible and otherwise things are fine.

I'm trying to fix this iMac for someone who's down on her luck. Anyone
have any ideas as to what might have gone wrong? Does this look like it
might be a simple fix or a minor adjustment, or is the CRT hosed?