The combo CDRW /DVD on my Optoplex GX270 suddenly stopped reading from anything other than a DVD. In fact it does recognise cd's it had written previously but it will not read past the root directory. Message says cannot read files.

Does not recognise CD-ROMS at all.

I have reset NVRAM and reloaded factory defaults and done a system restore to date before problem. I have loaded latest firmware. I have tried different disks to rule out disk problems. 

Any help appreciated.