Please see this link if you are using Windows and this link if you are using a Mac for troubleshooting steps available.
If you are using a Mac and the issues relate to your tax file, please see how do I find my tax data file (.tax file) in Mac for possible locations you can look for on your computer to recover the original tax file.
There is also a possible solution provided by a customer in this thread that you can try if the first link does not assist. Essentially, look for a file named "unsaved TurboTax document" to locate your .tax file.