Black fullscreen, constant lagging

[Trains]

Hello!
I've played Rimworld on my laptop before. But yesterday, I made a clean install from win 10 to win 8.1, because my laptop had worked really slow with win 10. Rimworld worked perfectly, so I didn't expected it to have any problems with win 8.1 as it's way more stable. Yeah, I was wrong.
I've downloaded the game again, and wanted to play, but when I started the game, the screen was black, just the game's cursor was there. The game runned, and the little image was there when I moved the cursor over it's icon, but the screen was black. I navigated myself to the options, and switched to windowed mode, and it solved the problem, but I'm curious, why I can't play in fullscreen mode.
Another issue, why is my game so slow? Like, in the main menu, when I make a new colony, ingame, everywhere! 10-15 FPS max. I've tried to search for solutions, but I haven't found anything. When I used win10, the game run smoothly, even at 3x speed. Now, it's so laggy that I can't even choose a landing location, because I can't scroll on the world map. I have no mods, and as I said, my computer was able to handle the game. I don't have a single save file, and almost nothing else on my laptop. What can be the problem?
Thanks for your responses, and sorry for my bad English.