Do you have to connect to Steam in order to play Portal 2 for the PC?

I recently purchased Portal 2 for the PC, during the install it told me to create a steam account, after doing so it asked me for the game key but when I type it in it just says "Steam Server is Unavailable", the Steam site says its likely because of my wireless connection, but its only solution I saw was to connect directly to the modem, which is a floor away in my house and I really don't want to haul my desktop, monitor, etc. down a flight of stairs or go and buy a 60+ foot ethernet cord for a two second test. is there any workaround I could use. If it makes any difference I only intend to play the campaign mode of the game no co-op or online needed