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.
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Why would I need to do that? Is it to get the bug information?
Well you wrote:
I don't know if it's the computer's or Minecraft's fault, because it only does it on this computer.
The debug crash would give us information about your system specs.

Options -> Touchscreen mode -> Off
Options -> Multiplayer -> Chat -> Shown
Ok, I fixed it, kumasasa. Thanks
Please force a crash by pressing F3 + C for 10 seconds while ingame and attach the crash report here.