Servers dont work

Logged on one on 1.6.4 time and found i couldn't go onto a server. Thought it was a problem with that server but tried all others and didn't work.
I tried it on 1.6.2 and it still happened. I looked online about what it said and minecraft forum said it might be a problem at mojang. Also tried it without my mods on it and still couldn't get on a server.