Lenovo - Troubleshooting - X200 and Booting from an External DVD/CD Driver
Just a short FYI to those of you who use the Lenovo X-series of laptops. Within the user's guide of the Lenovo USB 2.0 CD-RW/DVD-ROM Combo II Drive (Part Number: 40Y8686) is a short paragraph stating the following:
"The standard USB bus power can be used in some configurations to power the Combo II Drive. For maximum performands in all configurations, the recommendation is to use the supplied power adapter."
You MUST attach the power supply in order to boot from the external drive. If you do not, it will appear to work, but will merely click at you.
Just want to save others from being quite frustrated because this does not seem to be clearly stated in the users guide.