you can check here if your cpu supports or does not virtualization:
(that link is in KVM manual also on MT wiki)
also, check if you have enabled virtualization in PC's BIOS. Some motherboards require newer BIOS version for that to work correctly.
Also, someone mentioned XEN - it was discontinued at version 4.4 and is not recommended for use and should be avoided.
KVM configuration can only be done through CLI and for that matter also API, but there are no such possibility from winbox and webfig at the moment.