minecraft launcher flashes between online and offline

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What I expected to happen was...: 
About 2 days ago my minecraft stopped working. It keeps flashing between online and offline mode. And when I manage to launch the game, it falls on the bar and only works in the background.
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What actually happened was...:
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
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