Open up the case and have a look.
Make sure the data and power cables are connected.
Take a look in the BIOS. Does the bios recognize that the device is present?
Take a look in the device manager (control panel). Is the device there? Is it enabled? Does it need drivers (look for a little yellow exclamation)?
The device may have failed. I have had it happen in the past. You will need to ask a buddy if he can test your ODD in his machine, and potentially test his drive in yours.
Alternatively, take it to a local shop. They would have the equipment to rapidly diagnose a problem.