Computer running slow? Diagnosis it here.

Diagnose 75% of common causes of computer slow-ness with one short article.

If your computer is running slow, it’s likely the result of either adware or a hardware failure. Of the two, it’s far more likely to be adware.

Before trying to diagnose and fix the problem, however, your first step should always be to ensure that all of your data is backed up. Slowness can be a warning sign of pending system failure.

Fortunately, keeping an up-to-date backup of your information and data is easier today than it used to be. There are a number of online backup solutions which are simple, effective, and incredibly cheap.

I personally recommend (and use) Backblaze ( For $5 / month, Backblaze maintains a complete and automated backup of all the files on your computer. In the event of a system failure, retrieving your data is as simple as logging in to their website and downloading it (or paying to have all your data overnighted to you on an external hard drive).

However, online backup software has its limitations. Depending on the amount of data you have and the speed of your internet connection, it may take as much as several weeks for the initial backup to complete (after which time your files will be backed up nightly).

Once your data is safe, we can try to figure out what’s causing the problem. But before we do, let’s dispel a few myths:

  • My computer is running slow because I have too many programs installed. Status: myth. With a few qualified exceptions, your computer’s performance will be unrelated to the quantity of applications you have installed. The number of applications running can be an entirely different matter. More of this later.
  • My computer is running slow because I have too much stuff / music / pictures. Status: myth. As long as you have at least 10% of your hard drive available as free space, your computer’s performance will not be noticeably affected by how much “stuff” you have on your hard drive. If you’re concerned that you may be running out of space, check by following these instructions.
  • My computer is running slow because I have a virus. Status: unlikely. It’s been years (literally) since I encountered a computer whose primary problem was a virus. However, there are other related classes of software (especially adware and spyware) that are common and will bring your computer to its knees.

Broadly, there are two possibilities: hardware failure, or a software problem.


If you get lots of pop-ups when browsing the internet, or if your browser exhibits odd behavior–such as clicking on a link and ending up somewhere other than you expected, or having your search results redirected to an unfamiliar search engine, then the odds are good that you’ve got adware (that is: software that is designed to expose you to advertisement).

Adware is software designed to expose you to advertisement. It differs from a virus in that whereas a virus is designed to harm your computer, adware is designed to turn you into a revenue stream. Most users expose themselves to the risk of adware by downloading and installing seemingly innocuous applications like free screensavers, smileys, or games. Visiting pornographic websites similarly exposes you to a high risk of adware infection.

If you think you have adware, remove any unwanted programs that start when your computer does. Then, do a system scan using Trend Micro’s free, online HouseCall application. If HouseCall identifies many “infected” files, you’ve identified your problem.

If you’re infected with adware, the only reasonable and reliable solution for you, as an end user, is to wipe everything out and restore your computer to its factory state. Alternatively, you can bring your computer to a repair shop, and expect to pay $100 – $300 for the shop to attempt to “clean” your PC. If the shop is unable to clean your PC (as is often the case), the shop will wipe and reload your computer for you.

I advise strongly against trying to use anti-adware utilities such as Ad-Aware, Spybot S&D, or Bazooka. Three reasons for this. First, even with a best-case scenario, it’s typically faster to wipe and reload than to spend hours running repeated scans–often simply to realize that you need to wipe and reload anyway. Second, the odds of you successfully resolving your problem with such utilities is quite low. Adware and anti-adware utilities are in a cat-and-mouse struggle. Adware is typically in the lead, meaning that even the best anti-adware utilities are typically unable to remove the newest varieties of adware. Third, there’s a chance you’ll just make things worse, owing to the proliferation of fake anti-adware utilities which are, themselves, adware. Differentiating real (Ad-Aware) from fake (Super PC Cleaner!) isn’t easy.


If your computer is running slow but isn’t bogged down by adware, you may be experiencing a hardware failure. Most cases of hardware related performance lost owe to one of two culprits: a failing hard drive, or bad capacitors. Diagnosing either is relatively quick and painless.

A failing hard drive can be reliably diagnosed by running the CHKDSK utility (instructions here). If you run CHKDSK once and it finds and corrects errors, this is normal. If you run CHKDSK a second time and it finds and fixes additional errors, this would indicate a failing hard drive. If you run CHKDSK a third consecutive time and it finds more errors, your hard drive is failing. Turn your computer off immediately and bring it to a repair shop that can (attempt to) clone your disk to a new hard drive.

Bad capacitors (or, bad caps) are rare, but can slow a computer system to a grinding halt. The only way to diagnose bad capacitors is to open up your computer and look. If any of the capacitors are bulging or leaking catalytic fluid, you’ve found your culprit (if you’re unsure what you’re looking for, watch this YouTube video). Though possible to repair, in most cases you’ll be better off replacing your computer with a new one.

About Mark Egge

Transportation planner-adjacent data scientist by day. YIMBY Shoupista on a bicycle by night. Bozeman, MT. All opinions expressed here are my own.
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One Response to Computer running slow? Diagnosis it here.

  1. Carter Parks says:

    First of all, I like your suggestion on going straight to the format when you have AdWare. You know I like to format.

    One note I do want to make (despite the fact your article is mostly targeted to PCs) is that on Macs, you really need 20% free space on the hard drive in order for the operating system to automatically defrag in the background. This of course is much more pronounced when your memory is maxed out and your computer is relying more on your page file.

    And on that note, if you feel like your computer is slow, make sure you have maxed out the memory in your computer. This is generally the cheapest way to make a major upgrade in performance. makes it easy to determine what memory upgrades are available for your machine.