Luke99999 wrote:Someone installed the OS in the USB drive
OS? What OS? Are you booting your host from the USB drive?
Luke99999 wrote:then I created a new virtual machine which boots from the usb drive
If *you* created the VM, then you should know the administrator password for the VM.
Luke99999 wrote:For this reason I cannot log on as an administrator in the OS.
You do not need to log in as an administrator in the host, only in the guest. You install the Guest Additions in the Guest, the VM. Since you created the guest (VM) you should know the administrator password.
I'm not an administrator on the computer I use, I'm a simple user. But on my VMs, the ones that I created, I am an administrator.