Question

I found the window .(split into two sentences)

Answer 1

The answer is as follows.

I made a discovery (sentence 1). It was the window (sentence 2).

Sometime, splitting a single sentence into two or more sentences, gives it more meaning and makes it easier to understand.

Answer 2

Upon splitting the sentence into two there will be two different sentences which will be following:

I found. And the other one is The window. These are two complete sentences in their own.

There are many such sentences which can be split to make a single sentence.

Thus, you can practice more such exercise to brush your skills further in English.