If you purchased the most recent records produced by Sony by Celine Dion "A New Day Has Come", Shakira "Laundry Service" and Jennifer Lopez "J To Tha L-O!" (but others recently released use the same protection) keep them away from your Mac with a CD or DVD player: they may be indigestible.
When you insert one of these "cleverly" protected optical media protected by the record company, the CD is not recognized but above all the Mac refuses to eject it and reboots, when the CD is already inserted in the boot machine with a gray screen.
The problem is due to the fact that the CDs thus protected cease to be true Audio CDs because they do not respect the format universally recognized by the players: in fact, instead of the CD Audio logo, the record companies insert an inscription "Will not play on Mac / PC ".
Since once inserted, the disk prevents the system from responding, the only way out is manual ejection or a restart with the mouse button pressed until the disk has come out.
A special page of Apple's knowledge base indicates several alternative solutions for those who have Mac OS X installed and want to force their startup.
1. Restart the computer, if necessary with the reset / interrupt button. 2. Immediately after the startup tone, press and hold the "X" key until the computer has finished starting up. 3. Open iTunes or DVD Player in the Applications folder. 4. Click on the Eject button in one of these applications.
The other alternatives are those of manual ejection with a paperclip and finally that through Open Firmware that we let you consult directly from the Apple page.
What is important to underline is that the eventual "failure" of the non-opening of the drawer of the optical reader is not an intervention covered by the guarantee because it derives from the use of a different support (the Audio CD which in reality is not 'an Audio CD) from what the Mac was designed for. The Mac obviously will not break or fail but in case you cannot reopen the CD player yourself with the indications provided above and those of the page mentioned, the repairer could charge you for the intervention. Better obviously not to use the offending CDs and to act with caution in the autonomous removal of the cause of the problem.
This topic has been discussed for some time in this Macitynet forum page.