Hi there!
Last night I went to play Minecraft and my game started to crash after every 5 minutes of playing. I restarted my computer in hopes of it helping. The game continued to crash. I deleted and redownloaded the launcher, and when I signed back in, the launcher told me I was only able to play the demo version. I have had my Minecraft account for a long time now and I don't know why this is happening.
Hello! This appears to be a duplicate of MCL-16570. Please see the Moderator Note on that ticket for a potential fix to your issue, and if that does not help, you could contact Community Support (linked in the Moderator Note on that ticket).