Have you looked on your "multiplayer options"? maybe some are off.
If that doesn't fix anything, try getting a new "version file" of your minecraft.
The following steps describe my way of doing it, if it doesn't work for you, don't blame. And if you are using mods before doing any of these things, try to login with an unmoded version of minecraft. Sometimes mods can create some conflicts with other functions that are there by default.
Note: this is for non-moded minecraft. I assume that people that have modded their minecraft in the past know how to get a fresh copy.
To do so, go on the minecraft folder, (you can access by clicking the button "go to ressourcepack folder" on ressource packs options), then go back on folder path and go to the versions folder.
Find the one you use, do a backup and delete it.(backup the entire .minecraft folder if you are a bit afraid of what could happen)
Then, simply go and open your launcher and, select a profile that use the version you just deleted and press play. It will re-download the version files and fix all conflicts that could possibly exist inside your minecraft folder.
It should fix some problems if it's due to the minecraft file itself.