Try holding down the power button for 5–10 seconds to force a shutdown. Wait a few seconds, then turn it back on. If it's a specific app, try forcing it to close (Alt+F4 on Windows, Command+Option+Esc on Mac).

A slow computer can be caused by too many programs running at once, low disk space, or pending updates. Try restarting your computer to clear temporary memory, closing unused browser tabs, and running a malware scan.