You have to clarify whether you used TurboTax Online or the CD/Download TurboTax software for the past years that you are looking for.
The tag below your question indicates that you are using TurboTax Online. If that's what you used for the past years, reinstalling your operating system has nothing to do with it. If you can't find your past tax returns you are probably signing in to the wrong TurboTax Online account. VolvoGirl told you how to get a list of all your accounts.
If you used the CD/Download TurboTax software for the past years, the tax returns are only on your own computer. You cannot access them in TurboTax Online. If you have the tax return data files (*.taxyyyy) on your computer, you have to reinstall the TurboTax software for each year in order to open the old returns. But when you start the reinstalled TurboTax program, it will not automatically find the old files. You have to click "Find a Tax File" and navigate to where the file is saved. Also, if your tax return files include a state tax return, you have to reinstall the state software before you can open the file.
