help! the annihilate button doesn't appear!

when i go to the new galactic war screen, there is no start button. this shows what is happening: please help.

You are probably using a broken mod. That, is exactly what happens.

this is the first time i have started the game and i don't use mods

you need the dpi scaling mod, your screen's too small

if "screen too small" is the problem you probably can get the PTE, it has a native scaling option.
see: http://exodusesports.com/guides/exodus-explains-planetary-annihilation-pte/

Hah, yeah, the button is somewhat further to the right than your screen is allowing for you. See above for your solutions; I would heartily recommend the PTE option

The minimum resolution for the game is 1280x720.
The PTE-build has a scalable UI, however I think the minimum resolution is still 1280x720.