You know the symptoms: your computer gets loud as the fan kicks up to high gear, the text you were typing takes 30 seconds to catch up, programs start opening slow or not at all, and the constant spinning of that hourglass or beachball. Your computer has slowed down a lot suddenly. You could wait for it to catch up (which could be never), you could restart it (and lose time and work) or you could find what is dragging everything to a halt and close that down.
Something is draining almost all your CPU or your Memory, and when that happens there’s not enough left for all your other tasks to function properly. It could be anything, but typically this is a left-over browser process that didn’t close out correctly, some run-a-way Flash code or a piece of streaming media that got stuck in the background.
On a Windows computer you can hit CTRL+ALT+DEL and then start the Task Manager from here right away. Once you have that open check out the Processes tab. In here you click to sort by CPU or Memory to get the processes running the highest to the top. If you see something running off the charts in relation to the others, then you’ve probably found your culprit and can click on it and then click to end the process.
On a Mac open up an application called Activity Monitor. Once in here you can also sort by CPU percentage or by Real or Virtual Memory. If something is running much higher here in relations to the others you can click on that and then quit that processes.
When you view these screens keep in mind the CPU is measured as a percentage and if your computer is suffering noticeable slowdown, if it is being caused by a rogue task, that task is probably causing both the CPU and Memory to spike so you should be able to easily find it. If nothing stands out, then there may be some other cause you need look for. If your computer also suffers from frequent slowness, there is likely another issue behind it.