Your numbering system is very confusing. I couldn't understand that the first question refers to 2 minutes and 3 seconds in the video.
Anyway...
1) "it" is the same "it" in "if it can't earn its keep". So what do you think "it" is? :)
2) We need the proper quote. "it may be the world's biggest [backyard fence to talk over]". Imagine neighbours chatting and gossiping over the backyard fence.
3) Look at this page, v.intr definition 3.
http://www.thefreedictionary.com/compute
When computers were relatively new in popular culture (on TV and film... we're talking about the 70s and 80s here), if a computer was unable to accept a question or calculation, it would say "Does not compute". This became a catchphrase for a while.