Computer not responding. Frozen software. PC locked up.

Hit Ctrl-Alt-Delete.  If nothing pops up or it is slow, something is wrong.  If Ctrl-Alt-Del doesn't show you anything, try hitting the Windows key on your keyboard.  Sometimes the Taskbar hides above where it can be viewed on your monitor.

All of your programs are listed on your Task Manager. To close a program, right-click and End Task.

Could be Safari or another browser is using all of your CPU. Sort by CPU percentage in your Application Tasks list so the highest is on top and determine what is running. Only games run full tilt for longer than a few minutes, so make sure no programs are pegged at 99 or 100%.  (It will show it pegged at 49 or 50% on a HT or dual-core CPU.)  If a program is loading or closing, it may take 100% of your CPU.  If you closed a program, but it is still listed here and/or using 100% of your CPU, right-click and End Task.

If this doesn't help and if you still can't do anything, look for a program called Explorer.exe.  End the Task.

Now click File -> Run in Task Manager and type Explorer.exe to restart it.  It should find it automatically and the PC should act like it is booting again.  The taskbar loads and your tray icons will populate.

At this point, your PC should be fine.  If your computer is still not responding, start closing your programs one by one.  It could be a toolbar extension or a printer driver that is loaded.  Check the Event Viewer or System Console to see if anything is noticable.

If you have questions about how to do this with the Event Viewer or other Administrative Tools, check Google for the settings according to your operating system, as it differs between XP, Vista and Windows 7.

Once you have performed these tasks, update any programs that are having issues, and restart your PC.  Once you have fixed the problem, clear your Event Logs so that future errors are easier to spot.

If your PC is not responding, you can also try rebooting into Safe Mode. Continually tap the F8 button on your keyboard when the computer is booting to get to Safe Mode. At that point, your PC should allow you to control it without anything else running. Check the Registry Run commands and other tasks from my Optimization article above. Also, search Google for specific malware infection information: search for the name of the malware to find the fix.