What happened to my preexisting profile?

We can't tell which profile you're talking about (Windows? Office? Microsoft Edge? something else?) and we don't know what "like I've never been here" means and we don't know if you've seen any error messages, or what you were doing on the computer prior to this issue, or any recent changes you've made to your computer. So it's random guessing at this point. If you can fill in with more information, we'll try to figure out what may be wrong.

Here's my guess: You've been working in a temporary profile up till now which, as the name suggests, is not a regular user account but a temporary state provided so you can use Windows tools to solve a problem with your regular user account. Being only temporary, it doesn't save any data you put there.