Firt of all, if you're running Minecraft on a PC, try redownloading. Tekkit as well. Same for both. Don't click Run when you firt download it. Leave it alone. After that, find the actual Minecraft application and double click it or whatever to open it. Then, all you need to do is wait. If it's over 5 minutes, conclude there is a compatibility or coding isue with the game. In that case, you'll need to contact Minecraft or your computer company for support. After that, there's really nothing you can do.
As for the browser version, you're computer (this may also have to do with the actual game running funny) may not be able to handle the resource intensive processes of running the game. If you have a good computer, well upwards of 2.6 GHz and 2GB of RAM, then we can obviously assume that it's a coding issue and not a hardware issue.
God lucK!
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