How to hide the cmd window to keep working on Windows
How to hide the working hashcat cmd window, I am afraid of closing it by accident when I work other things, and I don't want to be disturbed by the cmd window, I mean how to run it backgroud
well, not sure what you want, but did you try ctrl+windows_key+D 
Opens a new desktop. 

The way back is ctrl+windows+left_arrow...
Google an app called "TrayIt", enables you to put any window into windows tray by double right clicking the close button.