Can not find my configuration of minecraft, and it wants me download something I have already downloaded.

I tried to play minecraft today, having played the game last night. I recently downloaded the PC version ran by Java and have thoroughly enjoyed the experience until now. I can not acess my world at all, for some reason when I am trying to launch minecraft, it wants me to download 1.12 version, which i already downloaded. So I am assuming that I will not be able to acess my world again, and am therefore deeply unhappy. I want to know what has happened and what can be done ASAP, otherwise I will be returning my copy of minecraft and getting a refund, which I am entitled to do as I havent had the game for too long.
Having tried to open minecraft. This is the information I was given.
Name: ga_ie.lang
URL: http://resources.download.minecraft.net/4b/4b0d1056b5ba0beac72e2fdf108d3455a8c35e84
Error details: Attempting to move successful download to C:/Users\Conno\AppData\Roaming\.minecraft\assets\objects\4b/4b0d1056b5ba0beac72e2fdf108d3455a8c35e84 The process cannot access the file because it is being used by another process
Filename on disk: 4b2a-dd75-8792-8051
Path: C:\Users\Conno\AppData\Local\Temp\4b2a-dd75-8792-8051
Exists: file
Please sort this out asap.