Login Problem: Cannot contact authentication server

When I try to log in with the right credentials, which work on mojang.com and with the old launcher, it should log me in.

It tells me that my credentials are wrong and I don't have the right Username and/or password, when I am positive I do. I was logged in before this happened, but I could only play offline.

Here is exactly what I do:
1. I open the launcher.
2. I put my username and password in.
3. I hit the login button, but It doesn't work.