You don't even have income unless you actually take the withdrawal from the 401k. If you just let it sit to grow earnings, you won't have any income to report.
If you do take the distribution, and this is your only income, you won't owe income tax and aren't required to file. But since the trustee will issue a 1099-R form, the IRS may send you an automated letter if they can't match the 1099-R to a tax return. You will probably save yourself some hassle if you file a return.
If your income is less than $31,000, you can file using the Tax Freedom edition, which includes complicated forms not normally included in the free version. It's a different web site for contractual reasons. https://turbotax.intuit.com/taxfreedom/
