My MineCraft game used to do this also. But first i must know, do you have the downloaded game, or do you play it in the browser?
If you play it in the browser, their is honestley nothing you can do, it is either that the browser game is down, or your computer can't handle the data that is sent into your video card on your motherboard.
If you have the downloaded game. You must delete all files that have to do with MineCraft,(Java,and minecraft itself)
But make sure that you don't delete your save game data, unless it's not important to you. Then redownload Java first. Then redownload MineCraft. After that start up the game, then go to your settings and look if the cpu usage is set to high or low. If it's on low, set it to high.
If you set it to high, it will be able to use as much computer memory as possible to run.
(I am a nerd )
-Arctic

thanks arc

i give it a try

Just delete your minecraft bin folder and everything should work fine.