how did you burn the ISO to the CD? what program did you use?

If you have K3B installed you can use that... open K3B, got to "Tools"
then choose "Burn Cd Image"... K3B will do a checksum for you to make
sure the ISO is ok.

if you don't have K3B installed and can't install it on 5.04, try
these suggestions
https://help.ubuntu.com/community/BurningIsoHowto#head-41d485cd1f4a2902492b7e5dc\
c1991af2ec8f564

If all that doesn't work, do you feel comfortable with a terminal window?

if you 'cd' into the directory or change the
"ubuntu-7.04-desktop-i386.iso" part to say
"/home/james/downlods/ubuntu-7.04-desktop-i386.iso" or where ever the
ISO is...

cdrecord -v speed=4 dev=/dev/cdrom ubuntu-7.04-desktop-i386.iso

I hope that helps, I think you burnt the ISO file to the CD as a file
and not a filesystem... or the cd is corrupt, either way try burning
another like I detailed and let us know how it works or if you have
any other questions.