SDL Community wrote:
...The problem is that your DPI and screen resolution is not sully supported yet. So the solution is to either change the DPI to 100% and then run the installer (the buttons are currently just off the screen) or, what may be easier in this case, but copy the plugin to here:
c:\Users\[YOUR_USERNAME]\AppData\Roaming\SDL\SDL Trados Studio\12\Plugins\Packages\
Then restart Studio...
Paul's workaround suggestion should do it, but it might be worth mentioning that this issue and some others have already been fixed in the source code version hosted on GitHub, so it is probably only a matter of time before the fix gets implemented into the released version of the installer. Of course, another option in the meantime for anyone so inclined is to download the source code of the installer and build it (with a free copy of Microsoft Visual Studio community edition). Then "install" in Windows the newly-built version of the installer.