I've written this info to help all those other unfortunate souls in my position! It took me a good 6 hours and a dozen reboots to get to the bottom of the problem, I hope it makes your search quicker. I have a DVD-ram drive and a DVD ROM drive. Windows Explorer assigned both drives letters correctly and changed from DVD drive to CD drive when a CD was inserted. Neither drive could read read any CD or DVD discs except DVD Movies and incorrectly identified all other discs as being formatted in RAW format. I put up with it for ages before deciding to try and sort it out as I just knew it wasn't going to be easy. Nero could still write and verify DVD and CD discs OK so I was pretty sure it wasn't the hardware. I uninstalled Nero, Itunes and several other possibly iffy programs then reinstalled re-installed Nero but that didn't help. I then used the helpful little program from Microsoft. "DeleteLowerAndUpperFiltersForCDDevices.msi" to remove upper and lower filters! After reboot that improved matters slightly. I could now read UDF formatted CDRW discs too! I then realised that DVD videos are also recorded in UDF format. So I had a system that could recognise UDF formatted discs but still not CDFS discs. Google pointed me to earlier posts on this site when I started digging. I took a look at the system information. Programs, Accessories,System Tools, System Information. Under "Software Environment", "System Drivers" I noticed that "cdfs.sys" was "disabled" and "not started" and that there was no File location entry. A search of my hard drive showed that it was not in the windows/system32/drivers directory where it ought to be. However there were copies of it elsewhere in the windows\servicepackfiles\i386 directory (and elsewhere) so just out of curiosity I copied the file into the system32/drivers directory and rebooted again. Problem sorted! I hope this helps as nobody else seems to have posted quite this fix. I have a sneaking suspicion that the XP SP3 upgrade may have caused the cdfs.sys problem but I have no proof of that. Dominic

... well done "DominicO" ... and labeled "CDFS File System Driver Disabled" ... excellent !! Grrrr "...pentathol makes you sing like a canary" ... got brain freeze