Have you installed mods and when you login you are getting a black screen? Or are you just getting a black screen when you login even without mods? Well this tutorial is the right one for you! This is a tutorial for Windows Computers. I am using Windows 7, so I don't know if that makes a difference to the other kind of Windows users.

1.) Force update Minecraft.

1.5.) If that doesn't work, open the start menu in the bottom left corner of your desktop.

2.) Type in the little bar %appdata%

3.) Click 'roaming'

4.) Open .minecraft

5.) Open the bin folder

6.) Open the minecraft .jar (You need WINRar or 7Zip. I suggest WINRar. They are both free, however.)

7.) Find the file that is named METAINF. It should be near the top.

8.) Right click the METAINF and click delete all files.

This should fix your problems. Please give me a diamond in the upper left corner of this post if this helped!