Cd-r readable on mac from pc

I have a pc connected to the internet, and a second hand mac with 8.6 on it. My problem is that I had a cd with system 7.6 on it, and decided to install some extra software because the computer didn't seem to have it. The problem was after I did this the computer would'nt recognise cd-r's from pc anymore which it could before I did it.after I realised this I deleted some stuff related to the insallation I did to try and fix it. I think some files may have been replaced or over run, or there may be an over load of different extensions going on. I downloaded the 8.6 updater which I hoped would fix things around and install the correct software to have it where it was before, but no luck. Could you help me in trying to fix this problem, I have tried most places like www.info.apple.com which normally help me, but this time they didn't even say how to fix it. Cheers
Alasta