Well, My Dear Watson, this may be a case of dwindling Laser Power. As the optical device gets older, it is not unusual for the laser to loose its original "brightness". It could also be that the lens is dirty. I have a G3 that will NOT read Gold colored CD's! You have not mentioned if the non-reading iMac can read commercially produced CD's. You only mentioned CDRWs so the assumption is that it can. Commercial CD's use a different technique in production, they are not all burned, many times they are either "stamped" or Layered. If the CDRW is produced using a laser which is "not up to spec" there is a possibility that the "pits" are not being burned deep enough to register with another "not up to spec" CD reader. A replacement CDROM can be had on eBay for a small(ish) sum and are quite easy to replace.
Hope this helps
I have two Rev-A Bondi iMacs, both pre-owned by different users. Their spec is identical, and all the components are original.
So why is it that one CD-ROM drive will recognise CDRWs, but the other won't? CDRs are no problem, and it doesn't make a difference if it's Mac OS standard or ISO 9660.
I've checked the extensions, software, control panels, everything I could think of! What am I missing?
Thanks for your help so far!