Getting a huge amount of errors regarding contained definitions in GameObject

I’m fairly new to Unity, but this one strikes me as particularly weird. Suddenly, all my scripts are getting similar errors. Here’s a snippet of one of them:

GameObject b = Instantiate(arrayOfPrefabs *as GameObject);  //Cannot convert from 'GameObject' to 'UnityEngine.Object'*

b.transform.SetParent(transform);
b.transform.position = transform.position; //‘GameObject’ does not contain a definition for ‘transform’ and no accessible extension method ‘transform’ accepting a first argument of type ‘GameObject’ could be found

Color c = b.GetComponent().color;
c.a = 0;
b.GetComponent().color = c;
if (b.GetComponent())
{
c = b.GetComponentInChildren().color;
c.a = 0;
b.GetComponentInChildren().color = c;

b.GetComponentInChildren().text = “sdf”;
//‘GameObject’ does not contain a definition for ‘GetComponentInChildren’ and no accessible extension method ‘GetComponentInChildren’ accepting a first argument of type ‘GameObject’ could be found
}
In some of these there’s also the following quote: “(are you missing a using directive or an assembly reference?)”, but my using statements are the same as they were when this code worked, it kind of happened all of the sudden, all at the same time. I tried reimporting all assets but it served for nothing. I’m absolutely lost, any help would be greatly appreciated.

Are you sure you haven’t declared a class called GameObject in your project?