Please insert disk into drive

Please help!
I think that I have tried everything, but may have missed something.
I have a SONY DW-U54A drive in my PCG-GRT916Z laptop and get the message: Please insert disk into drive E: in explorer with a CD inserted.
If I start Nero, I can copy the CD or make a disk image and see the contents of the image.
I have stpped every running process from the task manager but still no joy on reading the CD.
If I put in a DVD that I have recorded all is well and can read the disk but when I put the CD back in explorer still shows the contents of the DVD that was in previously. Refresh does nothing and if I select one of the files (from the DVD listing with the CD in the drive) I get a box saying Cannot open… Make sure the disk is in the drive you specified.
Any ideas?

Why does this always happen with laptop drives?