When you click play on steam a page pops up with the four options play support options and exit. When you click play it goes into full screen and the logos go by and the game starts up. I've played 21 hours decently problem free, however today when I get to the screen with the four options and click play, it goes away, and after awhile it says steam is preparing to launch fallout four and that same screen With the four options comes up again, and I click play and it just cycles again. I've tried many times and it always does the same thing. I've already tried uninstalling and reinstalling the game but that did not work. I have no idea what I did differently this time from last time that would cause it not to work. If anyone has a solution to this i'd strongly appreciate it.

OK, Firstly, this issue is [censored], we've all been there, 30 different drivers, reinstalled 20 times, i just about lost a kilo of hair with stress, lol.
Secondly, my computer is not under-powered, please check the minimum specs before anything else. I have a i53330 @3.80GHz, 16GB ram, multiple SSDs, and a GTX 960 4GB.
Thirdly, I tried many "tips" to get it working first, including altering my ini which did nothing lol.

So, basically, right click the fallout 4 icon on your desktop, then go to properties.
Now, make sure that it isnt set to open as admin in the "compatibility" section.
Next thing to do is navigate to Documents (my documents on older systems) to find your "My Games" folder.
Find the folder named "Fallout 4" and delete it.

Open the game and enjoy... at least i did. Good luck and have fun guys

You really need to stop copying and pasting this lol.