Using the TurboTax online editions, only One tax return can be completed per account and User ID. If you used the same online account to do another tax return, then the first tax return is gone.
Go to this IRS website for free federal tax return transcripts - https://www.irs.gov/individuals/get-transcript
For a fee of $30 you can get a complete federal tax return from the IRS by completing Form 4506 - http://www.irs.gov/pub/irs-pdf/f4506.pdf