minecraft doesn't recognize my world

Usually my game gets slow or crashed, so the only alternative I have is to restart my computer, by doing this the game performs a "restart" as it remains as if it was installed for the first time.
The last time I had to restart my computer, I was entering my world and just when I had already loaded it crashed, so I restarted the computer and when I entered Minecraft my world disappeared, I searched files and the world is still there but the game does not recognize the world