It sounds like you deleted the Dell hidden partition that could hold information that allows the CD to boot properly? Some Dells have a hidden partition that holds bios information, as well. That is why I asked what system it was.
Do you try hitting the F12 key when the Dell splash screen comes up, which should give you the boot media options? You may need to hit it several times to catch the option, at the splash screen.
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"I love it when a plan comes together." - Hannibal Smith