On your Mini 9, restart it and enter the BIOS setup by pressing "2" and make sure 'legacy USB' is enabled. Save it. Now, reboot and select the boot options list by tapping "0" at startup and choose USB Storage, now the system should boot to either the USB flashdrive or the USB DVD/CD drive, which ever you are using but keep in mind that the Mini 9 only has one 'powered' USB port (usually located next to the power adapter socket) and using another USB port might not supply enough power to an external DVD drive, and even the 'powered' USB port sometimes doesnt even have enough power to power the DVD drive depending on the DVD drive chosen, the best thing is to either use a DVD drive with an external power supply or just use a USB thumbdrive which would eliminate this scenario altogether...hope all this helps ya