I just installed Portal again, I was going to download the updates for it which stopped me playing it last time. I go to open steam to start the updates and steam starts updating the main client, stops at 0% and says "Steam is temporarily unavailable, please try again later." 

So I can't even get into the steam client at all. What should I do? I cant really try again later because my data cap resets tonight and I wanna download quite a lot of stuff I've been meaning to.