Computers BIOS doesnt recognize CDROM and freezes when booting from USB?

I need to install Windows XP on my computer (Dell Optiplex GX260) which has a formatted C: drive. In my BIOS, the boot sequence has CD ROM listed but says (not installed) beside it. So I tried booting from a usb boot drive and I changed the BIOS accordingly, but after the start up, the computer hangs on a blank black screen with a blinking white underline in the top left corner. HELP!