Network access to VirtualBox VM from Network PCs

If you just used the default Network settings in your VM, it will be NAT with DHCP. That means you get a LAN IP from your VirtualBox DHCP Server and you can't really access the machine from the outside.

Check out the VirtualBox Manual on Networking: https://www.virtualbox.org/manual/ch06.html#networkingmodes

I guess bridged neworking should be best. You should configure a static IP address.

EDIT: Concerning the edit removing "host-only networking": It's true that you can't see the VM from outside. But you get virtual interfaces (vboxnetX) on your host machine. So if you route it through, it should work. The setup is more complicated, but the VM is less exposed.