Black sims, walls and floors when zoomed out and on certain angles

Whenever I load my saved file, the game runs smoothly but after several seconds, my sims as well as the walls and floors suddenly turn black. It also affects the whole neighborhood. I noticed that the error only shows when I zoom out (see photos attached) and when I move the camera on certain angles. This seems to happen only the first floor of my house (the second floor walls and floors don't turn black when I zoom out and change the angles). 

I have already read and done the possible fixes shown in this thread, went through some of the threads with similar problems as mine (and also did the solutions such as lowering the graphics, enabling laptop and windowed mode) but it didn't help my game at all. I have CCs and I have all the expansion packs. I have been playing for more than 3 weeks now and this is the first time I encountered this error.

Here's my computer's DxDiag:

Operating System: Windows 8.1 Single Language 64-bit (6.3, Build 9600)

Language: English (Regional setting: English)

System Manufacturer: Dell Inc.

System Model: Inspiron 5548

BIOS: A07

Processor: Intel(R) Core(TM) i7-5500U CPU @ 2.40GHz (4CPUs), ~2.4GHz

Memory: 8192MB RAM

Page file: 4057MB used, 5329MB available.

DirectX Version: DirectX 11

Thank you so much.