Minecraft – If I can’t login to the launcher and I can login to Minecraft.net and servers are on, what do I do

It's possible that the Mojang Authentification servers were just down for a bit. You can check the status of the servers on https://help.mojang.com/ or http://xpaw.ru/mcstatus/. https://twitter.com/MojangStatus might also be of helpful to check. If the servers are down, there is nothing you can do on your end, and it's up to Mojang to fix it.

If the problem persists even when the servers are up, make sure Minecraft is not blocked by any firewalls. On Windows, you'll need to allow both java.exe and javaw.exe. I suggest deactivating your firewall for just a few seconds to check if that is indeed the problem before trying to fix stuff that is not broken.

Every time I have experienced an error similar to this, it was as a result of server maintenance and the issue was resolved less than 30 minutes later as soon as their servers were back up. You could go to an online minecraft chat room, like the one in planet minecraft for example, and see if anyone else is having the same issue at the same time that your are. If the issue is not a result of mojang's servers being temporarily down I can't troubleshoot that without more information.