I've tried all the suggestions on here, but without any success. However, what I did find was that the 'missing' CDs are in fact on my iPhone (I did a spotlight search) and have been imported, but just don't show up on my iTunes!!!
Another baffling Apple anomaly. I must say that iTunes in general is very poor. Transferring from iPhone to iPhone is often made very difficult. Music bought and paid for via iTunes can not be listened to on non-Apple products, yet if it is downloaded illegally and for free it can be listened to on anything (explain that one). And lo and behold if your PC which has your iTunes on it breaks (which they do) or needs replacing. In most cases, you lose everything.
It's the typical attitude of a manufacturer which has got far too big for its boots and thinks it can do anything and we will all keep buying. Look at Ericsson and Nokia (in Europe at least). Even the design of the phone is very out-of-date now. Check out the Sony Z1 to see real innovation.
This will be my last iPhone if it stays like this (which I suppose it will). I'm off to Android. Much easier, less big brother and much more fun.