If you have more than one optical drive you should try the other one and go back through the F12 menu.  The Dell BIOS will normally boot only from the master drive.
  My Dell 8250 is running slow after years of use. I have Windows XP Pro and have all the current updates. I wanted to reinstall XP using my Dell reinstall disk that came with my computer. I did all the data backups, removed all compeating software (anti-virus, etc.) and unplugged all the peripherals. Then I started the computer with reinstall disk in the drive and hit F12 when the “Dell” logo appeared. I was greeted with 6 choices; #3 was IDE CD-ROM Device. I selected it and then was given a choice of F1 or F2. “F1” did nothing but repeat the same screen. F2 took me to a BIOS setup screen. I rebooted and tried to access the disk through Windows. The official looking screen gave me the choice to install XP. I selected it. Then a pop-up message told me that I could not install because the version on my computer was newer than on the disk (duh).   I'm willing to go through the steps to reinstall all the service packs, etc. I just want to start fresh. Any suggestions?   And yes, I've gone through the Microsoft AND Dell instructions to reinstall. I'm stopped before I get to the second step.   Thanks.   Mike 
Dell 8250 reinstalling XP problem