This sounds a bit like data corruption, I would start off by running a test on your Hard Drive / SSD. You can find information here on how to do so. Also, be sure to let us know if you see a found.001 folder or similar in the root of the C:\ drive.
If not data corruption, I suspect you may have been far behind in keeping the latest updates installed or you have a really old computer. Please let us know your Make / Model
The fact that your data disappeared is worrisome, I would navigate to the c:\users folder to see if there are any duplicate user accounts, or if you are using the wrong account, or even if the user profile became corrupt and you are now using a temporary profile which I have seen Windows do in the past.
Lastly, do you have more than one storage device on your computer, eg c:\, D:\?