It's not possible to view US TV channels or sites like Hulu online if you are outside of the US, due to international viewing rights and laws preventing it. So, if you try to watch, say ABC, online from the UK, the site will recognise that you are not using a US IP address and will block you from watching it.
Same goes if you try to watch UK channels online while in the US - I'm in the US right now, just arrived yesterday, and if I try to watch the BBC iplayer or ITV player online from here, I just get a message saying that the content is not available from my location.
One way to get around this is to view the sites using a proxy site or VPN, which masks your IP address and makes it look like you are in the US.