This might be a bit touchy...if this starts a Recovery function, cancel out by pressing Esc or opening the cd tray.
Press Ctrl + Alt + Delete to restart.
At the options screen, choose the option to Start with CD-ROM Support...it should be the default selection. If it is not, use the arrow keys to select it and press Enter. If it starts the setup, we'll be ok...if the recovery options starts, post back. It will plainly tell you if it is a recovery operation...