Minecraft Stuck On Demo

I bought the game about 4 months ago, and I was having fun with Minecraft Java Edition.  And then yesterday I opened it to play Minecraft once again: and the game wasn't opening.  It was saying that I already had the game open.  I looked in the task manager and it was running - but there was no window of Minecraft, so I tried ending the task.  Then it told me that there was an unknown error trying to run it.  I tried switching versions, and it did not work.  I went on help.minecraft.net and then read that I could uninstall and reinstall Minecraft.  I tried that and when I reinstalled it, it said "PLAY DEMO" instead of saying "PLAY".  Also, instead of saying my Minecraft username: Nubby_Playz it said "Player".  I tried logging in and logging out, and still the same thing.  I would like to get some help as soon as possible.

Thanks.