DVD-RW showing as CD drive

Hey there
Ok, here is the jist - I've been using my DVD-RW for ages happily burning media away, using it as a drive, not a problem. All of a sudden it decides it no longer wants to burn.
Now, if you put a DVD in it - with data or video - it works fine. It shows up in Windows as a DVD drive and the data can be accessed, not a problem. There is a slight problem with the sound but then there always has been and I use it for movies so little this is the least of my worries. However, when you pop a blank DVD in it, it bizarrely changes to a CD drive. The emblem in Windows changes and no application will allow you to burn it, or even access the drive. It's really weird. After hunting around the internet I tried many things like upgrading the firmware, checking properties, etc. etc. but to no avail. I basically gave up and resigned to the fact that it must be my DVD drive was knackered.
So today I bought a new one. Hooked it straight up to my PC, replaced the other one, it showed up as a DVD drive which excited me but a little too soon unfortunately becuase as soon as I put a blank disc in surprise surprise it all changed again to a CD drive. Now Windows only recognise it as a CD drive.

There is obviously something wrong with my PC rather than the drives themselves to be causing this. If anyone could offer me the slightest bit of helpful information I would be extrememly grateful. And I do mean extrememly.

Thanks a lot guys