Weird chat/mouse bug (solved)

When I try to pick up an item, by clicking on it in my inventory, it doesn't. And when I try to chat, it says "cannot send chat message." I don't know if it's the computer's or Minecraft's fault, because it only does it on this computer. If it is the computer's fault, please tell how to fix it.

Fixed: The chat was set to Commands Only and Touchscreen mode was on.