Go to the location where you store your VM /home/ron/VirtualBox VMs/Semios Win7 /.Open .vbox in your favorite text editor to check if it is empty. Probably it is 🙂 In the same folder you should have file Semios Win7 .vbox-prev. Copy the contents of this file to Semios Win7.vbox, save, and try again.

Source: virtualbox – Why is my virtual machine inaccessible? – Ask Ubuntu