Hey Aetcho,

While it is understandable you want to get the problem resolved as fast as possible, bumping up your own topic won't speed things up any faster for you or us.

Here's a quote:

If

You see an error like:

Exception in thread "main" java.lang.NoClassDefFoundError: com/mojang/minecraft/MinecraftAppletThen

You didn't read the instructions, and download then install the minecraft.jar file.

To fix

Go back to the instructions, download minecraft.jar as instructed and place it in the correct directory.

If this didn't work, you might want to try and update your Java Software if possible. The only solution I can provide if this fails to work is to re-install your java and follow the instructions on our website again.

Hope this helps,

~Scoopade

When ever i try to use it dosen't come up with the login details it says "failed to run minecraft" I don't know what to do can anybody fix this problem?

Ok, first of all, I am in agreement with everyone saying the spamming is annoying, but I'll try to help anyway:

If your problem is like many of ours, open your lib folder, create a new folder, title it "minecraft.jar", and extract the contents of your downloaded minecraft.jar file INTO this one. 
If you open your lib folder and see a whole bunch of .png files from the download, that is your problem.  The system is looking for a folder called minecraft.jar, not a collection of random files which should be in the .jar

I hope this helps.  If not, I can't really say I'm sorry.  Go look in the earlier help forum topics and find your error, like the rest of us resourceful  people did.