You need to be using a TalkTalk router (with at least 5Mbps speed) connected to your YouView box. Switch them both off at the mains for a few seconds and then put them back on. If your TV Boost chanels don't appear from 301 onwards, you can try going into the TalkTalk Player, and then going to My Boosts. It should show up in there too.
The boosts are usually ready to go the morning after they are activated on your account.