I only can use minecraft.net for playing (Because I can't get the World of Minecraft client to work, help me on my other forum topic), and minecraft keeps locking my keyboard up.

What I mean is that sometimes when I click blocks, the mouse gets stuck and I can't move it around. I try using commands with the keyboard, but the keyboard is useless, because when it locks up, it's like it's unplugged. The only thing I can do is to hit the power button on the computer it's self, and that's not a good way to shut a computer off. Only one time it went "The window 'Minecraft' is not responding. Would you like to force quit this application?" And I forced the mouse so hard because the warning was on the minecraft screen, which the mouse gets stuck on, and it kept going back to the center, but I finnaly got to get it to click 'yes'. Also, on my Windows side, it locked up when I was using the World of Minecraft client! This is so weird! I use Iceweasel on my Linux to play Minecraft. Can someone PLEASE tell me how to fix this?