How do I fix boot error "Kernel requires a 86-64 cpu"?

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http://askubuntu.com – My desktop pc gives the following error when trying to install from a cd: Kernel requires a 86-64 cpu only detected a i686 cpu unable to boot My pc is a Medion, 160GB hard drive, Pentium 4 processor, 512MB memory. I'm installing Ubuntu 12.04 from the (complete manual magazine). (HowTos)