Could not connect to server

Can't login to the MinecraftLauncher:
Everytime I try to login to my minecraft-acc theres an error called:
"Could not connect to server."
Thus I am just able to play singleplayer in the offlinemodus.
Version (On the bottom left): "2.0.800" (Is this the right version? If not, where can I change it?)

I reinstalled Minecraft three or four times now, but there is still the same error message. Can somebody help me?

greetings

P.S I am able to login on the Mojang Website, but not in the MinecraftLauncher or Minecraft.net