You might have a root assassin in your system
Part of the explanation can be that Ubuntu loaded some firmware
You should click enable networking to get the options I think (once you've done it you can't do it again and it is a bit hard to remember everything exactly
You have to tell us more facts.
The minimum is exactly which Mint you have - which version and which edition
(main or any of the CEs)
We also need to know a bit about all your hardware.
Run " lspci " in a terminal and post here (to avoid misunderstanding - the first character is a minor L and you copy by marking with the mouse and then right click)
Some wifi and possibly built in sound can be connected to USB even if they are internal - if you suspect you have one of these run " lsusb " in a terminal.
Also tell us if this is using mint4win or not, quite important