Seamless Mode and Auto Resize Guest Display are grayed out (disabled) - VirtualBox

I am using VirtualBox version 4.3.12 and I am using a freshly installed Windows 8.1 VM, but for some reason i cant get it to go into seamless mode.

I have seen that some people have said that i need to install guest additions on my guest, but when I go to install it, it just says this:

enter image description here

And when i click on that, it just does nothing. Would anyone have any ideas? This is really my first time using VirtualBox. Any help would be much appreciated. Thanks!

As the menu states, the "Insert Guest Additions CD Image" inserts a disk image on a virtual CD on your machine. This virtual CD usually starts automatically with autorun, but if not, just go to "Computer" and launch the "VboxWindowsAdditions" exe file on the CD and follow the installation.

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