Enable VT-x in your BIOS security settings, ensure that your Linux distro has working KVM module. code example

Example: this computer doesn't have vt-x/amd-v enabled. enabling it in the bios is mandatory virtualbox

docker-machine create -d virtualbox --virtualbox-memory=4096 \
    --virtualbox-cpu-count=4 --virtualbox-disk-size=40960 \
    --virtualbox-no-vtx-check default