I'm assuming for what you said, you are learning Linux, so I'm going to explain briefly every command. But consider Reading the man [command] pages of every command before using it.
I'm assuming that your daemon is not working, but just for make sure, check out you BIOS network configuration, maybe the Wireless antenna is turned off.
You installed a new eOS so I'm sure you didn't touch the root user, so first we need to configurate that, now open a terminal type SUPER + T and write this command:
$ sudo passwd root
Then enter the password you want, note that root is the god user that can do literally everything in you Linux machine... we need to log in the root user for managing the daemons without problems, I don't recommend using sudo with your user even if is admin because it really doesn't have all the privileges of a root user at all. So for loggin into the root user just type:
$ su root
and enter the password you already typed.
Now we need to reconfigurate the networkmanager.service so for that...
# systemctl disable NetworkManager.service
# systemctl enable NetworkManager.service
# systemctl restart NetworkManager.service
So with that done we basically restarted the service, now type exit and reboot your computer. Note the # that means that you are using the root user and not the standard user reprecented by $ this thing is used in most of Linux webpages so keep an eye for that.
Now finally if for some reason, you aren't watching the tray wifi icon, enter the terminal again and type:
$ nmcli dev wifi connect "NAME_OF_YOUR_WIFI" password "type_password"
And yes write even the " this method is used because in bash (Linux console) when you enter SPACE means you are using a command or parameter(this is called pipeline, not sure). When using the " you are telling the console that you will enter a string and evaluate if it is exactly the same coincidence (string = word/sentence).
Now you're done, if for some weird reason you are still unable to use the wireless, let me know, please don't use the root user for common things like installing programs, the root user is only for manipulating other users and special kernel configurations such as daemons and hooks.
You can learn more about Networkmanager commands here.
Another method is using the iw network program, so for installing it...
sudo apt install iw
but is probably you have that already installed, so first we need to know the name of your Wireless card, for that type
iw dev
the output will show you something like wlan0 use the same name of that for the next command... now finally for connecting to the internet type and hit ENTER
iw dev wlan0 connect "name_of_wifi"
the screen will turn blue and will ask you for the password, that's all I know for fixing that kind of problems, hope this will work.
UPDATE
I think Windows is spoiling your BIOS, I can't explain why but my friends done this...
Enter a terminal, and type sudo nano /etc/default/grub
and add this piece of code acpi_osi=Linux, where it says : GRUB_CMDLINE_LINUX_DEFAULT
so it will turn into GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux"
that parameter tells grub to take full control of the computer hardware when there are others OS in the hard disk.
Exit and save changes to the file with CTRL + X
and update the grub with sudo update-grub
GRUB is a boot loader package that supports multiple operating systems on a computer, it handles hard stuff with the kernel, we don't want to know ;)
