Strange but real reasons your PC might be going a bit a slow:
Your PC doesn't get enough fresh air.
No, I don't mean you should do all your work on your PC al fresco. But you should keep the vents on your computer clean and free of dust, hair, carpeting and dirt. Air is needed to keep your PC cool, as overheating can affect performance - and even damage the heat-sensitive electronics inside. Regularly vacuum around the vents or use compressed air to clean them.
Your laptop is on your... lap. Or any other soft surface, like your bed, the sofa, or cushions. Soft material can block the vents and cause your computer to overheat. And as we know, that can lead to sluggish performance and even hardware damage. Always work on clean, hard, flat surfaces if you can help it. And for men, having a lot laptop on your lap can decrease your chance of being a father! (See this Discover article.)
Things are loose on the motherboard.
This is especially likely if you've gotten a memory upgrade, but even computers direct from the factory can come with loose memory chips. If you don't feel comfortable opening up your PC and checking to see if the chips are plugged in, bring your PC to the store you bought it from (or to a trusted technician) and see if they can put them in place.
A messy desktop is not simply an aesthetic problem. Items on your desktop use up a bit of your PC's memory. Organizing your files is one of the easiest ways to free up a bit of wasted computing power.
Turn off life-support for crashing programs.
Windows generally is like a sensitive doctor who has a hard time letting programs go. Usually when a program is non-responsive – something that happens a lot with slow PCs – Windows, by default, gives it a ridiculously generous 20 seconds to respond. This lag can cause other programs to stall, triggering a cascading collapse of other apps. You've got to be tougher than Windows, and have it automatically close any program that stops responding.
(CAUTION: the following directions involve tampering with the registry. Always make a backup before changing the registry, and proceed with care.)
To have Windows automatically close unresponsive apps, click on Start, go to Run, and type regedit. (If a window asks if you'd like to continue, click Yes.) Next, find the correct key on the left sidebar of the new window. It should read HKEY_CURRENT_USER\Control Panel\Desktop. Now, the last step: double click AutoEndTasks, and then bump the value from 0 to 1. Presto: no more life support for crashing programs.