Update: 5/27/17 GMX File:
This code deactivates everything on screen, except the message that pops up on screen.
This code along with the code above will allow the message to pop up and the object you want to appear on screen too. You can have multiple objects pop up if you want, just copy and paste this code below as many times as you want.
instance_activate_object( your object name);
This code below will make every object active again.
Note: You could make a pause button using this code if you want, one button that reads pause, when pressed will deactivate all objects, except want you want displayed on screen.
Next, you can have a resume button, when pressed activate all objects or create a inventory using this code.