Having the same problems, its probs not you or your end but maybe something to do with steam itself.
I have had it all this week, all I can say is keep trying and it will eventually work. I am not sure
of the reason but I fixed it by deleting the clientregistry.blob in the steam folder which I found out
to do by reading this thread on the steam forums.

Though doing this does fix it, but the problem still comes back after a while etc... could be the high
traffic they are having these days as its a holiday period, im not sure.

Welcome to Armaholic Merry Christmas to you too.