win 8 64 won't install on 32 vista dell inspiron 531

Hi, I have been given a dell inspiron 531 with 64 bit AMD processor, running 32 bit vista home basic, that has responded well to RAM upgrade to 4GB. I want to install 64 bit win 8 pro media centre which I have on an original MS CD. either over current vista or on separate partition as dual boot. For some reason the dell wont read the MS win 8 64 disk (or any other original MS OS disks...