How do I find out why my taxes are still pending with IRS?

[tamconroy]

I e-filed a few days ago, the same day as my sister and hers have already been accepted. The IRS says something isn't right with mine but I have no idea how to find out what's wrong.

[CatinaT1]

Once your return is filed, TurboTax has no control over the processing of your return or the release of your refund.

Here are a couple FAQs to track your refund:
When will I get my federal tax refund?
How do I track my state refund?
Why does Where's My Refund say "approved" but TurboTax still says "accepted"?

Why do some refunds take longer than others?

What if my IRS refund is taking longer than 21 days?