VirtualBox fails on startup
Result Code: NS_ERROR_FAILURE (0x80004005) / Kernel driver not installed (rc=-1908) are the errors displayed when the kernel driver needs to be recompiled. It usually happens when updates to Ubuntu are installed.
The kernel driver can be recompiled by issuing one the following commands:
sudo /etc/init.d/vboxdrv setup
sudo /sbin/rcvboxdrv setup
The former one works for Ubuntu versions prior to Ubuntu 16.04. If the first one is not found on your system, try the second one.