Well it sounds to me as though you're not actually booting off the CD's and it's trying to load whatever is/was on one of those disks previously. You need to make sure you're setup to boot off CD, through either a couple ways:
1) If your BIOS supports it, you might see a thing when you first turn it on that will tell you to press a certain key for the boot menu. For Dell's it's generally F12 I believe. This would be the quickest way to try and verify it's booting from CD.
2) If you don't see anything like that, go into your BIOS setup and look for a menu that refers to the boot order. Change it so that your CD-ROM or whatever media you're trying to boot from is above BOTH of the hard drives (or just the word hard drive if it doesn't list individual devices). Then reboot. You'll still need to press a key when it says "Press a key to boot from CD-ROM...." or whatever it says so keep an eye out.
If you know both of these things already I'm sorry but have no idea at this point what could be wrong.