When a program stops responding entirely
A frozen window that won't close normally, no matter how many times you click it, is exactly what "End task" is for. It forces the program to shut down immediately, even if it's completely unresponsive to normal input.
Finding what's actually slowing your computer down
When your whole system feels sluggish rather than just one app, clicking the "CPU" or "Memory" column header in the Processes tab sorts everything by usage, instantly surfacing whichever process is consuming the most resources.
Frequently Asked Questions
If I end a task, will I lose unsaved work?
Yes β "End task" force-closes a program, so any unsaved changes in it are likely to be lost. Try to save your work through the program itself first whenever the program can still respond at all.
How do I see which program is using the most CPU?
In the "Processes" tab, click the "CPU" column header to sort every running process by usage, from highest to lowest.