Dave - pleased to report a successful result! I followed the resolution advice given in the MS knowledgebase link to delete the two particular values from the relevant registry key, and after a reboot I could immediately access my D:\ drive again (the CDRW/DVD drive) and it's working perfectly. I'm really grateful for your excellent advice on this one - and my donation to the site will follow (actually its overdue really as I've had plenty of good advice from here, but better late than never

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The cause of this problem seemed to be exactly as described in the knowledgebase. A while ago I tried to install an old version of Easy CD Creator but found it was incompatible with Win XP and had to uninstall it, but it left some drivers behind which Win XP would prevent from loading at startup and display a message to this effect. I posted here a few weeks back for help with finding and removing these drivers, and thanks to Bold Fortune I was able to identify and delete them from my System32 folder, but I guess these two registry values were still there. So now it looks like all traces of Easy CD have finally gone - thanks to you guys - great work!