Gateway not booting (black screen) - can be booted without internet access?

I sometimes have the problem, that when powering up the gateway it boots not past a black screen.
The grub loader appears, some boot text, but then black screen before the KDE surface.
then I reset the machine and most often it boots normally. But not always.

I think it is because the host was sometimes not connected to an internet. But this is just a guess, I tested it right now with internet connection and it did not boot.
Question: Can the Gateway be booted without internet access? Without being connected to a WLAN/Ethernet? (tor does not work obviously, its booting to KDE surface only)

(changed Gateway to 1 GB RAM)

Yes, it should boot fine without network access.

Black means totally black without any text?

Can you change virtual consoles? (Platform-specific Desktop Tips)

Edit by Patrick:

See Kicksecure ™ in VirtualBox - Troubleshooting - Kicksecure ™ does not Start?

black without text. Will try when I am at my machine next time.

No, it does nothing. Just a black screen.

Sorry, its not the workstation, its the gateway.

gateway has not been modified, except RAM. No additional packages were installed. No response on the consoles. Just black.
I let it run for a few hours, nothing but one CPU of the host system is constantly at 100% load because of virtualbox. No other VMs running.

Even a reset did not work.
I had to power down the VM. Now it boots flawlessly.