Usage of "do" in "why do I want to do something"

Phrase:

Maybe you'll ask why do I want to lift my keyboard off my desk.

Question:

Microsoft Word says that I should remove the "do". Why is that? I think the "do" should stay there.

Generally, I tend to use the verb construction "do want" when I am trying to make a contrast to what I don't want.

I don't want a boss who will hold my hand. What I do want is a boss who will let me learn from my own mistakes.

I'd agree with Microsoft - unless you are contrasting to reasons why people don't want to lift the keyboard, I'd drop the "do" from the sentence.

Maybe you'll ask why I want to lift my keyboard off my desk...

If you'd like to keep the word "do" in your sentence, I'd suggest one of the following, depending on whether the reader is asking themselves why they'd lift the keyboard or why the author would lift the keyboard:

Reader asking self:

Maybe you'll ask, "Why do I want to lift my keyboard off my desk?"

Reader asking author:

Maybe you'll ask why I do want to lift my keyboard off my desk.

Why do I want to lift my keyboard off my desk?

But

I was asked why I want to lift my keyboard off my desk.

Reported Speech

Ignore what Word says. Better yet, turn off Word's grammar checker; it's designed for American English native speakers, not for English learners. It's loaded with zombie rules to make Americans feel less anxious about never being taught grammar in school.

As for what it's flagging, there are two issues involved.

The first one is Do-Support, which provides a meaningless auxiliary do when an auxiliary verb is required by some construction like Negation, Wh-Question-Formation, or Tag Formation, viz.

• I want it. ~ I don't want it.
• You want it (at some place). ~ Where do you want it?
• You want it. ~ You want it, don't you? ~ You don't want it, do you?

The second issue is the construction you present. It's an embedded question, a type of complement clause that is the direct object of ask. In embedded question constructions, the usual Subject-Auxiliary Inversion (as in What did you ask?, with Do-Support) is normally not performed, producing

• I don't know what you asked

instead of

• I don't know what did you ask.

That's what Word flagged.

However, it's wrong in this case because it didn't notice -- and has no way of noticing in any event -- that this is a situation where it's OK to do the inversion, and use the do. I recently dealt with this question here, and the rest of the explanation is in the link.