Help! can't read normal CD's.

[Small Moose Ltd]

Oh dear, this is a bit of a pickle,

The internal CD-ROM drive of my clamshell 466SE can only read Macintosh
CD's. For some reason it cannot read normal music CD's or CD's that have
been created with a PC. I've quite a few discs that have been burned for me
by a PC user containing .jpegs but every time I insert the disc it says

'This disc is unrecognisable, do you want to reinitialise the disc'?

Its also failing to recognise a DVD disc now, but I know the drive is
working because each and every time I insert a Mac formatted disc it works
every time. 

I think I might be missing that 'High Sierra ISO9006 extension thing, but I
also have a CD/DVD extension that says I don't need any of those other
things any more. 

I am running Mac OS9.1

Prior to everything going silly I had installed an old game from 1997 that
needed me to install an old CD-ROM driver to run it, so I created a new
extension set just for that old game, and I thought everything was fine.

Can anyone help please?