Reboot the computer and press the "DELETE" key as soon as you hear the beep.
On the top of the page look for the Boot TAB and selct it (use the arrows to navigate). You should have your floppy drive in first position. Your CD-ROM should be on second position and your Hard Drive third (change positions by pressing enter while the drive is selected and then use the + & - buttons to change the relative positions).
Go to the Exit TAB and selct "Exit Saving Changes".