If you used the desktop CD/Download editions installed on your computer, the only copy of your tax data file and any PDF's will be on the computer where the return was created. TurboTax does not store online any returns completed using the desktop editions.
If you purchased the software from TurboTax as a download then you can download the installation file at any time for any reason as often as needed for up to three years from the date of purchase. Sign onto your download account - https://shopping.turbotax.intuit.com/unified/downloads?route=myaccounts
You can also get free transcripts of your federal return from the IRS - http://www.irs.gov/Individuals/Get-Transcript
For a fee of $50 you can get a complete federal tax return from the IRS by completing Form 4506 - http://www.irs.gov/pub/irs-pdf/f4506.pdf
Sorry, if you used the Desktop program for personal returns or used the Windows Business program then the only copies of your returns is or was on that computer unless you saved a backup pdf file or .tax file somewhere else like on a flash drive, external drive or some backup location. You can get a copy from the IRS.
If you have the data files ending in .tax saved you can ask support for another copy of the program to install.