MissingMethodException: What the heck is this?

By the way: I'm a beginner at developing and coding, so if you know the answer to this please make it in a way i understand. I wish i knew these stuff like you guys :P

Around 4 months ago i was using unity for trying to make a game while following a tutorial. It was perfect before. I stopped using it because of exams, test, projects etc. Now since I'm done those things and its summer for me i decided to go make and learn how to create a game again. Since i uninstalled it i re downloaded it again on unity3d.com on the latest version (unity3d 4.3.4). This is where it stresses me. I load up unity and make a Terrain (GameObject-Create Other-Terrain) now once I clicked Terrain i get this annoying error "MissingMethodException"

MissingMethodException: Cannot find the requested method. UnityEngine.Terrain.get_InstanceObject () (at C:/BuildAgent/work/d63dfc6385190b60/artifacts/EditorGenerated/Terrains.cs:82) UnityEngine.Terrain.OnEnable () (at C:/BuildAgent/work/d63dfc6385190b60/artifacts/EditorGenerated/Terrains.cs:512) UnityEngine.Terrain:CreateTerrainGameObject(TerrainData) UnityEditorInternal.InternalEditorUtility:INTERNAL_CALL_SceneViewDrag(Object, Vector3&, Vector2&, Boolean) UnityEditorInternal.InternalEditorUtility:SceneViewDrag(Object, Vector3, Vector2, Boolean) (at C:/BuildAgent/work/d63dfc6385190b60/artifacts/EditorGenerated/InternalEditorUtility.cs:152) UnityEditor.DockArea:OnGUI()

Please help me!

Things i tried to solve this problem :

Create a new project - "Didn't work"

While creating a new project, only took some import packages - "Didn't work"

While creating a new project, I didn't take no packages - "Didn't work"

Restarted my computer - "Didn't work"

I did use some assets I got online and packages (Terrains, weapons etc) but once I saw the errors I was getting I removed the project. I made sure when making a new project it didn't have those packages.

So please I've been sitting here for 5 hours trying to fix this nothing works. Thanks.