If your BIOS is OK with the CDROM in first boot device and if the PC does not detect your CD, maybe the CD is bad. Do you have try burning another CD?
Maybe also your ISO file of Cassandra was broken, did you check the MD5?
K.I.S.S. ===> "Keep It Simple, Stupid"
"Simplicity is the ultimate sophistication." (Leonardo da Vinci)
"Everything should be made as simple as possible, but no simpler." (Albert Einstein)