Not to panic there, mate.
1> Go into your %appdata% and delete the Minecraft folder.
2> Open Minecraft
3> Add the saves and servers.dat files back in.

That should fix it. If it doesn't.. you may want to contact jeb_ on Twitter.

go to windows start(search programs and files) type %appdata% click on the .minecraft folder then delete then bin
reopen minecraft login and it will regenerate there for fixing it.

Delete it, and re-download it.

Bump*

My suggestion- Play minecraft in the browser window.

I think the biggest problem here that Nobody has addressed yet is that SpikeHunter here is trying to install an outdated mod on a new version of Minecraft.
SDK Guns mod hasn't been updated since 1.3.2 and has an extensive list of dependencies.
In short: You can't have SDK guns mod. You're better off deleting the /bin folder and starting your minecraft.jar over from brand new.

Also-- akanton: You mean the META-INF folder..?

have you tried to delete META-FOL before doing the test of the mof was installed?
META-FOL prevent mod to work and makes black screen on your minecraft when you come

Do you guys have any idea what you're even doing?

I use a Apple laptop, AND NO WINDOWS

First open Minecraft. Then, instead of logging in, click options. Then, it will say "Game location on disk." Click the colored text. Then, when your .minecraft opens, go to the very top of the Explorer window. Click where it says "Roaming." Then, delete the .minecraft folder.

Re-open Minecraft, and login. It should work now. If it doesn't sorry, I don't know how to help.

just try deleting the .MineCraft folder

i was typing in something but then plant minecraft decided to go down and deleted all my 2 hours of work :/.Will try to help later if i can

oh crap, well...

theres an equivelant to the windows button on pc(google it i dont know what it looks like) press that and r, then dig around till you find .minecraft, delete it when you find it.

OK, so press windows button and r on your computer, in the window that opens up type in %appdata% in there find .minecraft. Delete it, in force updating you are only updating the minecraft.jar and since you put the files in other files than your minecraft has been stuffed. deleting the .minecraft will fis this. Oh and once you have deleted it you can redownload it from the launcher.

I have a LAPTOP

Use an hammer and hit the pc when you eat cookie. Now turn it on.

Force updating doesn't work.

Got it.

From a guy who knows his way around mods, Make a copy of your saves, worlds, and your texture pack and screenshot folders if you wish. Once you do that, delete your .jar. Otherwise, you might want to delete your whole bin folder. If you try to install it again, Make sure you delete the Meta-Inf folder!

On Your MC Login page click options and click force update. Click done and log in. It Should work fine.

[deleted]

I had this issue recently while I was trying to get rid of connected textures. Delete your bin and open Minecraft.exe. Do this by searching the programs list on your computer and finding the file that way. Using the shortcut on my desktop instead of the Minecraft.exe itself did not work for me as it gave me the "not downloaded" error. Force update or simply login from there and minecraft will download a completely new bin.

On a side note, are there any error files on your desktop? It could be a java issue if every time you attempt to log in, it black-screens like that. I had some Java issues with these symptoms and Java always puts some handy dandy error reports and your desktop if that is the case.

Redownload minecraft if it isn't working

Restart your computer.

-1b8

Force update!
(in options, force update,login, then play the game)

Force update!
(in options, force update, then play the game)