Windows 8 Screen Resolution in VirtualBox [duplicate]
Something to try (assuming a Windows host):
- Stop VirtualBox (all VMs).
- Open a commnad prompt and navigate to your VirtualBox folder (something like "c:\Program Files\Oracle\VirtualBox\").
- Run
VBoxManage.exe setextradata "Your VM Name" CustomVideoMode1 1600x900x32 - Restart your Win8 VM and check to see if the resolution is available.
More info here and here
It seems like you haven't installed the VBox Guest additions. Once that is installed, it should scale to any resolution automatically.
Do remember to restart your VM after installation.