Game runs in full screen but cropped by window

Tried playing the sims 3 after a while (it's been over a year since I last played), but when the game launches the window size stays the same size as the game launcher (see photos attached). The logo clips & intro movie play at the corresponding size for the window, but once I get into the loading screen, world selection, and the game itself, that's all full screen and fully functional, but cropped by the window. I can load a save and access Options but can't change the resolution or window/full screen mode because the check to save changes is cropped out, so I can't change the window that way. I've spent some time searching for a solution but only found a handful of similar cases and none of the solutions seem to be working for me. (The most promising one suggested holding "Alt" while launching the game/pressing play but either it's not working or I need to hold it for like 5min straight?) 

I do have mods, but it was running just fine with them last time I played (and bc of mods, I launch the game with Run as Administrator, though I have also tried launching from the EA... thingy. to see if that works better. it does not.). I haven't touched the game at all since last February. I've moved so my pc is in a new physical location and we have different internet but that shouldn't be the problem.

Only other thing I can think of is I messed with my display settings for my monitor and drawing tablet a few months ago--used to use duplicated display but now I use extended with some finagling for the tablet screen to look higher resolution but I've never run the sims on the 2nd screen. I don't remember what the exact settings were prior to me switching to extended and what exactly the changes I made were so I don't know if I'd be able to revert back and see if that resolves it. 

My copy of the game was originally a disc install on a different computer, but with the whole EA account thing I was able to download it onto the current computer without the disc. Current computer is Windows 10 PC. My monitor resolution is 3840x2160 at 150%.  I have fully shut down my computer and started it again since the problem occurred and that didn't have any effect.

Please help!