There are many possible reasons why your computer could be running slow.  It is probably full of malware, or maybe it just needs some maintenance.  There's also the possibility that you hard drive is failing and you should backup your data right now.

Check the health of your hard disk drive

Before you get too far into cleaning up your computer, first make sure that your hard drive isn't failing.  The act of cleaning up the crap from your system is fairly hard disk intensive and could trigger a catastrophic failure if your drive is already on its way out.

Check the SMART status of your drives with a free tool like HD Tune. Scroll down the page to the free one, not the Pro one.

SMART data from a mechanical hard disk drive
SMART data from a mechanical hard disk drive

I have highlighted the interesting stats in this SMART report which HD Tune calls "Health".  Look to the "Data" column of those three particular stats.  If you see a number higher than 0, then I recommend treating your hard disk drive as "on its way out" even if the utility says its OK or Healthy.  The reason for this is that those highlighted stats indicate that the computer has had trouble accessing spots on your drive.  Usually when this starts, it gets worse over time, so get your important data backed up now and consider getting that drive replaced.

Now if you are happy that your drive is healthy and those stats are 0, or you have a SSD instead of a mechanical drive, then move on to the following maintenance and cleanup tasks.

Too much crap installed and running

Everything that starts up when you log in, or is running in the background is having an impact on how fast your computer starts and runs.

Tidy system tray - Not too much crap running
Tidy system tray - Not too much crap running

Check your system tray - The area down near your clock to see how much stuff is running.  Use the up arrow to see the hidden icons and hover your mouse over them to see what each one is called.  If you spot something that you know doesn't need to run automatically like uTorrent for example, then open up the program and go through the settings to find and turn off the "start when Windows starts" option.  You can also use the Startup tab in the Task Manager to disable unnecessary startup apps like OneDrive, OneNote, SpotifyWebHelper etc.

Go through your Programs and Features list and uninstall anything that you no longer use.  There are several ways to get to the uninstall programs list, you can find it in the Control Panel or run appwiz.cpl.  Don't just uninstall anything you don't recognise though, as some of that stuff keeps your system working.  Get rid of old versions of Java, in fact chances are you don't need Java at all.  Remove cleanup and speedup type tools if they weren't recommended to you by someone in the know.  Anything that has the words "ad", "coupon" or "toolbar" in the name can go.

Too many antivirus programs

Antivirus programs are fairly resource intensive and actually stand in between your hard drive and your programs so they can scan everything as it is accessed.  So it stands to reason that you don't want heaps of the things fighting with each other to scan everything.  You should have one antivirus program, and one active antimalware program only.  I'll discuss why and which ones in another article.  If you have more than one installed, then get rid of the old ones, they are really slowing your computer down.

This can often happen when you decide to buy a new antivirus but forget to remove the one that came with your computer and has probably expired.

Too many temporary files

Temporary files accumulate through normal use and can slow down your computer if left to build up.  There are several places that these files accumulate so its a good idea to use a cleanup tool to remove them all for you.

I like to use the free version of CCleaner, but I make a couple of tweaks to the default cleanup rules.  In the list of things to clean, uncheck the following things.

  • System -> Memory Dumps - Uncheck this because we can use memory dumps to diagnose bluescreen problems
  • Web browsers (Edge, Ie, Chrome, Firefox - You'll have to go to the Applications tab) - Uncheck Session, Recently Typed URLs, Last Download Location and Cookies (This is up to you, some people are scared of cookies.  I leave them there because if you remove them you have to log back into all of your sites again)

Hit run cleaner, accept the warning and let it do its thing.  The more frequently you run it, the quicker it will be each time.  I recommend running CCleaner every month.  If you purchase the Pro version, it will monitor and clean your disk automatically.

Funny side note: CCleaner stands for Crap Cleaner.

Hard disk fragmented

Defrag is probably something you have heard before.  Maybe someone told you you don't have to worry about it anymore, as Windows does it for you, or modern file systems aren't affected as much by fragmentation.  Those things are true, but a proper defrag can help and if you think about how it works, it makes sense.

Windows built-in defragmentation is a soft-touch approach, it really doesn't do much more than consolidate free space.  Which is handy, but it leaves files spread all over the drive slowing down access.  So lets do the job properly.

Note: This will take a long time and will slow your computer down while it is processing, so maybe set it before you go to bed.

Get yourself a proper defrag tool like Defraggler from the same people who made CCleaner.  Again the free one is all you need.  The paid one can be set to automatically defrag on a schedule.

Defraggler is as easy as choosing the drive to defrag if you have more than one and hitting "Defrag" then waiting, and waiting.  If you have Solid State Drives then Defraggler can "Optimize" these too without damaging the drive.

For more details on defragmenting you hard disks check my post: Should I defrag my computer

Too much malware

Chances are you have malware of some type on your computer.  I have a more complete malware removal guide here which you should check out, but in the meantime these quick steps can help you out.

Download and run the following tools - Tip, download them all ready to go before starting any of them.

  • AdwCleaner - This one will restart your computer when it is done.
  • MalwareBytes - This used to be a companion tool which ran beside your normal antivirus, but it is now a full featured antivirus itself.  Purchasing a full license to replace your existing antivirus is a good idea.

Run those tools in order.  As stated, AdwCleaner will restart your computer if it finds anything, and MalwareBytes may decide to as well.

This is not a definitive list of actions for removing malware but its a quick clean up and will get a lot of it.  There may be things hanging on tight that require more aggressive processes and possible more experienced eyes.

Unruly software

Sometimes a bug in third-party software can cause your system to slow down.  Perhaps a program you use is using more CPU time than it should, or thrashing the hard drive for some reason.

Task Manager - sorted by CPU usage
Task Manager - sorted by CPU usage

Check your Task Manager for processes that are using a lot of CPU time.  The easiest way to open the task manager is by pressing CTRL+SHIFT+ESC at the same time.  Once there, go to the "Details" tab and click the CPU field to sort the list in descending order by most usage to least.  As you can see on mine, there isn't much going on.  The System Idle Process should be taking the majority of the time.  If you see something in there sitting on a high number then it may be malfunctioning. If you recognise it then maybe check for an update to that product or reinstall it, if you don't recognise it, then get to googling or ask on the BleepingComputer forums.

Get a SSD

These things are great, and really once you use one you won't want to go back to a mechanical drive again.  A Solid State Drive has no moving parts and is super fast.  But they are a bit more expensive than regular mechanical drives and normally come in smaller capacities (unless you are rich).

The idea here is to replace your old slow mechanical drive with a SSD to greatly improve disk access speeds.  Windows boots and is ready to use in a few seconds rather than minutes, and practically everything opens almost instantly.

The downside to migrating from a mechanical drive to a Solid State Drive is that you need to completely reinstall Windows to get the most benefit from it.  It is possible to clone your drive onto the new SSD and get a considerable performance increase, but Windows really needs to be installed fresh on the drive to get the full benefit.

If installing a new drive sounds too hard, then get a computer tech to do it for you, or wait until you purchase your next computer and insist it comes with a SSD.

Conclusion

Some of these tasks require a bit of know-how but don't be afraid to give it a shot.  If you really feel uncomfortable about performing these tasks, then I recommend you call in a computer technician from a reputable company and get it all sorted out for you.  Maybe get them to show you how to do the maintenance yourself so you can keep it clean.