Minecraft freezes when logging onto certain servers. Windows says Minecraft is responding though.

I wanted to play a Survival Games server today but as I joined the server Minecraft froze. Widnows told me it wasn't frozen but after about 15 minutes of waiting, it was still frozen.

I had tried it with other versions and it did work. Other servers that weren't survival games servers, were not working also.

*edit* It now says took too long to log on but then as I try to reconnect, it tells me "failed connection, Error 503 of URL"
The URL has something about
http://session.minecraft.net/game/joinserver.jsp?user=spyguy439&sessionId=-1236399932243806077&serverId=-731ca7e5106e177a787c3d924a5fbc5d5e46cede