Written There are number of answers I've written on the subject of cleaning a computer, and they all describe the issue of cleaning both software and hardware.  But since I always have difficulty with finding my old answers on Quora, I will go through this one more time (and save the link for future reference).In the distant past (at least in computer years), PC meant any computer that was IBM based, using a Microsoft OS, whether laptop or desktop.  Currently, PC seems to mean your standard desktop unit.  I make this distinction simply because the two devices are dissimilar in how to open them up and clean them physically, and I want to clarify I am understanding the question as meaning the current definition.First, there is your physical cleaning.  Manufacturers of brand name computers all have proprietary case styles, along with configurations that may create some confusion.  So let's start with your basic setup, first:This is an image of an older model, but the outline remains relatively the same. 

There are three areas to pay attention to, though.  Your main focus is cleaning the cooling areas, specifically your fans and vent areas.  air purifier sprayIf you notice in the graphic, the CPU fan is just near the power unit fan and the rear vent.  air cleaner for carburetorThis is not always the case, and the power supply fan may be internal.best air purifier for cooking smellsAnyway, get yourself a cheap can of compressed air, or an air compressor if your more inclined to less harmful solutions. Basically, you want to blow down the inside of the computer.  Do this outside, since in many cases, the computer can sport a lot of dust in hidden spots.If you look really closely at the graphic provided, you will notice the cooling fins under the CPU fan are actually crusted with dirt. 

This is your typical computer killer, since it prevents the efficient cooling of the hottest part of your computer.  You can usually remove the fan from the heat sink by undoing the four screws that hold it in, not the ones the connect it to the motherboard.  You can see these here as holes in the black fan frame.  Once you remove the fan, a clean, soft bristle paintbrush can be used to remove that crusted dirt.You're done when you don't see any chunky dirt or ghost turds floating around.With some brand name models, a vent conduit may be placed on over the CPU to maximize air flow.  These are usually easy to remove, but you have to ensure you do to get the best cleaning.* For a laptop, the best way to clean internally is really just to blow compressed air into the vent outlet, usually located on the left side.  This should remove some of the dirt on your cooling surfaces.  To do a more thorough cleaning involves some dis assembly, and if you aren't comfortable with doing this, I would suggest finding someone who is.

Externally, just wipe down your surfaces with a damp rag, Windex or rubbing alcohol.  Keyboards may be a more complex issue, but removing the keys (and placing them neatly on the table in the same order they belong in will make for an easier reassembly) is not hard, just time consuming. Some longer keys may have a wire swivel attached to them.  Be gentle with these and don't lose the wire.  However, if you break something, keyboards are cheap and easily replaceable.Cleaning your OS is a bit more of an effort., select and install these programs:RevoMalwarbytes Anti Malwareone of the antivirus programs (only if you don't already have a CURRENTLY active antivirus).  I normally use AVG, but there are several good ones to choose from., download and install these programs:CC CleanerDefragglerRun these programs in this order to maximize your cleaning:Empty your Recycle Bin.  Just right click on it and tell it to empty.This is a program that uninstalls other programs better than their own uninstall utility. 

Select and remove any programs you don't use, or don't think you need anymore.  Revo will run the normal uninstaller, then find and remove any left over files and registry entries.  There may be some risk in doing this, but I use it regularly and haven't had any problems.There are several utilities in this program.   First, run the Cleaner by clicking on the analyze button.  This will look for stray and temp files that can be cleaned up.  After the analysis, run the Cleaner button. Click on Registry, then scan for issues.  When complete, fix the selected issues.  CC Cleaner will ask if you want to back up prior to the changes.  I have used this extensively, but have had one instance where the registry was damaged.Finally, select Tools, then Startup.  Look down your list of startup items and disable those you don't want to start when your computer does.  Things like Google Update, Java Updater, Quicktime Updater, and so on, can be disabled.  If you find something you're not sure about, Google the information. 

There are actually only a few things that need to start with Windows, so you can regain a lot of speed by turning off some of these startups.This starts clean without your disabled startups, and verifies everthing is working fine.  You can always run CC Cleaner again and re-enable the startups you want if something isn't right.Check for updates to your antivirus, then do a really good run with it.  * Lately, I've been seeing a lot of comments and answers claiming an antivirus is unnecessary, maybe even detrimental.  Don't listen to them.  Some programmers and other techs don't mind taking chances, but going without an antivirus is irresponsible, and can affect not only you, but anyone you connect to.  The alternative is much worse.Reboot.Check for updates to Malwarebytes Anti Malware, then run a scan.  This is not an antivirus, but will find certain types of spyware and other unwanted programs, often loaded by just visiting certain websites.n Microsoft Windows Update.  This will make sure you have the latest updates, including the malicious software removal tool.