Why is my mouse stuck at the bottom and my keyboard not responding?

Unplug the mouse and restart the computer without it. If you can use the keyboard afterward, try another mouse. If the problem remains, the mouse may not be the cause.

Do you have a game controller connected? Check that it isn't sitting somewhere with a stick or button pressed, or disconnect it and see whether the cursor stops moving on its own.

Try unplugging and reconnecting the mouse and keyboard, and check their ports for moisture or anything obviously out of place. If either port is wet, leave the device unplugged rather than reconnecting it while wet.