To use 2D Video Acceleration within , your host's video card should support certain OpenGL extensions. On startup, checks for those extensions, and, if the test fails, this option is silently grayed out.

To find out why it has failed, you can manually execute the following command:

$ VBoxTestOGL --log "log_file_name" --test 2D

It will list the required OpenGL extensions one by one and will show you which one failed the test. This usually means that you are running an outdated or misconfigured OpenGL driver on your host. It can also mean that your video chip is lacking required functionality.