Check if kvm-intel or kvm-amd depending on you system is loaded, type : lsmod | grep kvm
If not, check if you can load it, type for Intel CPU : modproe kvm-intel
If you got an error like : Error inserting kvm_intel (/lib/modules/2.6.18-194.26.1.el5/extra/kmod-kvm/kvm-intel.ko): Operation not supported., that's probably mean, your KVM support is disabled in BIOS ?
It's depend on your system, in the latest BIOS releases, you can enable/disable support to kvm.
To verify if KVM is enabled/disabled in BIOS, type : dmesg | grep kvm.
After enabling KVM in BIOS, type : modprobe kvm-intel.