Just a thought, you say you are using Bitdefender firewall and by rights, when you installed it, it should have disabled Windows Firewall. Just to be sure though, you may want to go to "services"...

I don't see where the OP is wrong, and saying doesn't really explain why he's wrong. Hiding the SSID is one of several methods to help secure a basically unsecured connection. "With the right tools"...

Sounds as if you are dealing with a problem connecting to the internet(?) and also connecting to your LAN(?). As for your LAN, are they all the same type OS's or a mixture. Are you using DHCP or...

No, you should not need a wired connection in order for the wifi router to work. The router, however, does need to be connected to the modem.

If you go to Control Panel > All Control Panel Items > User Accounts, does user 'Dasha' indicate that you are part of the Administrator Group? Alternatively, from the command terminal, type 'net user...