As Feckit pointed out. (though being part of a network or not has nothing to do with it) Just setup a password for your login.
Then each time you step away from your machine hit the
Windows key and L.
That will lock your workstation and require the password to be entered before you can do anything.
This will not put the PC into standby. Why do you think it will? :/
It will continue to run as if the screen is displaying the desktop it will not interfere with anything running on the PC.
Simple.
If your not sure i suggest you consult your system/network administrator.