If your bootup sequence isn't to check cd-rom 1st go into bios. The key to press on booting varies but it will say which one to press when booting up (usually a F key). Then look in each catagory for booting sequence (using enter key,esc to exit, and pageup/down to navigate). If you make a mistake don't worry as you can exit bios without saving. Change bootup to cd then just boot from Recovery cd. It should do the rest.