|First you need to get into the BIOS setup to see if your laptop can be set to boot from usb (if your external cd drive is connected by usb).|
If there is no 'usb' option in the boot settings, you will have to fit a new internal cd drive to replace the broken one. A laptop with a non-working internal cd-drive is pretty crippled anyway these days, even without your current problem.
To get into the BIOS setup you press a specific key as soon as you turn the laptop on. The key varies by make of laptop. Turn on your laptop and immediately look at the bottom of the screen. It should say "Press XX to enter setup" (XX will be the name of the actual key). On most laptops it's usually one of the 'F' keys.
If you need more help please continue posting. I'll help you all I can.