Dell Vista won't boot past BIOS screen

Hi everyone:

I have a Dell Inspiron 1720 with Vista. Days ago I remember downloading something that made my laptop reboot. Upon rebooting, I still can't get past the bios screen. (Actually I do, but only to a black screen with a blinking cursor.) I've pressed F12 to change the boot order to CD Drive. Ive inserted a vista bootable disk in and heard it spinning and working. Seconds later, I get an error along the lines of, "Not a bootable disk, press X to retry". I've tried the test that is available in the F12 setup, but no errors were detected.

Any help would be greatly appreciated.

Thanks, Dala