Is this a grammatically correct sentence? 10 points.?

Question:

きのう、わたしは　かき/Kaku　できません　でした。
Yesterday, I wasn't able to write

Answer:

If you are asking if the upper Japanese sentence is correct, no, it's not correct.

I think you need an object to make an accurate Japanese sentence. You were not able to write what?

Addition:
>It's kind of a general statement.
Like I wasn't able to write because I was busy is what I mean by the sentence. :S

Even if it sounds general in English, it's better to say "you were not able to write WHAT" to make an accurate Japanese sentence.

But if you want a general sentence, it's

きのうはかけませんでした。

You do not always need わたしは in Japanese.

I think you tried to combine かく and できません. But we use かけません as its combination in that case.

Addition2:
>So, could you say I wasn't able to write an e-mail yesterday?

If you want to say "an email", you say メールを

きのうはメールをかけませんでした。

>Still with the dekimasen deshita part to it?

You want to use できませんでした？

Another way to say it is, きのうはメールをかくことができませんでした。