What slows down a computer and how to fix it
A computer slows down when your hard drive fills up, too many programs run at startup, dust clogs the cooling fans, or malware consumes processing power. The good news is that most slowdowns come from fixable causes, not hardware failure. You can regain speed by removing unused programs, clearing temporary files, disabling startup items, and running a malware scan—all tasks you can do yourself in an afternoon.
The most common culprit is a full hard drive. When your drive reaches 85 to 90 percent capacity, Windows or macOS has nowhere to write temporary files, so everything slows to a crawl. The second is startup bloat: programs that launch automatically when you turn on your computer, running invisibly in the background and consuming memory. The third is dust buildup inside the case, which traps heat and forces the processor to throttle itself down to avoid damage.
Key Takeaways
- Delete or move large files (videos, photos, old backups) to an external drive or cloud storage to free up at least 15 percent of your hard drive space.
- Disable startup programs by opening Task Manager (Windows) or Activity Monitor (Mac) and turning off applications you do not use every day.
- Run a full malware scan using Windows Defender (built into Windows) or a third-party scanner like Malwarebytes to catch infections that drain performance.
- Clean dust from cooling vents and fans with compressed air every six months, or more often if you have pets or live in a dusty environment.
- Restart your computer weekly to clear temporary files and reset memory usage, which often restores speed without any other changes.
Free up hard drive space without losing files
Your hard drive needs breathing room. When it fills beyond 85 percent, the operating system cannot write temporary files, and performance drops sharply. Start by finding what is taking up space: on Windows, right-click your C: drive, select Properties, and look at the pie chart. On Mac, click the Apple menu, select About This Mac, then Storage.
Large files—videos, photo libraries, old backups—are usually the culprits. Move these to an external hard drive or cloud storage like Google Drive, OneDrive, or Dropbox. You keep the files but free up space on your computer. Delete the Downloads folder, which accumulates installers and old documents. Empty the Recycle Bin (Windows) or Trash (Mac) to actually remove deleted files. On Windows, you can also run Disk Cleanup: search for it in the Start menu, select your C: drive, and let it remove temporary files and old system backups.
Turn off programs that run at startup
Every program you install asks permission to launch when your computer starts. Over time, dozens of applications run invisibly in the background, consuming memory and processor power before you even open a browser. Disabling the ones you do not use daily can cut startup time in half.
On Windows 10 or 11, right-click the taskbar and select Task Manager. Click the Startup tab. You will see a list of programs with a Status column showing Enabled or Disabled. Right-click any program you do not need at startup—Spotify, Adobe Reader, printer software, antivirus updaters—and select Disable. Do not disable anything labeled Windows or Microsoft unless you are certain what it does. On Mac, go to System Settings, select General, then Login Items. Remove programs from the list by clicking the minus sign.
Be conservative: if you use a program daily, leave it enabled. If you use it weekly or less, disable it and launch it manually when you need it. You can always re-enable it later.
Scan for malware and remove infections
Malware—viruses, spyware, adware—runs in the background and consumes processor power, memory, and bandwidth. It can slow your computer to a crawl, hijack your browser, or steal passwords. Windows includes a built-in scanner called Windows Defender that runs automatically, but you can also run a manual full scan.
On Windows, search for Windows Security in the Start menu. Click Virus & threat protection, then Scan options. Select Full scan and click Scan now. This takes 30 minutes to an hour but checks every file on your drive. On Mac, the built-in XProtect runs automatically, but you can also read Malwarebytes (free version available) and run a full scan. If malware is found, both tools will quarantine or remove it automatically.
If your computer is severely infected—if it is so slow that even opening Task Manager takes minutes—consider booting into Safe Mode (Windows) or Recovery Mode (Mac) before scanning. This loads only essential system files and makes it easier for the scanner to detect and remove threats.
Clean dust from fans and vents
Dust buildup inside your computer traps heat. When the processor gets too hot, it throttles itself down to cool off, cutting performance in half. Cleaning the fans and vents takes 15 minutes and costs nothing beyond a can of compressed air.
Shut down your computer completely and unplug it. Wait five minutes for capacitors to discharge. Open the case—most desktop computers have a side panel held by two thumbscrews. Use short bursts of compressed air to blow dust out of the fans, heatsinks, and vents. Hold the fan blades still with your finger so they do not spin (spinning without power can damage them). On laptops, blow compressed air into the vents on the sides and bottom. Do this in a well-ventilated area or outdoors, because a lot of dust will fly out. Repeat every six months, or more often if you have pets or live in a dusty environment.
Restart your computer weekly
A restart clears temporary files, resets memory usage, and stops background processes from accumulating. Many slowdowns disappear after a restart because Windows or macOS has a chance to clean house. Make it a habit: restart your computer once a week, or whenever you notice it feeling sluggish.
Restarting is not the same as sleeping or hibernating. Sleep mode keeps your computer in a low-power state but leaves programs and memory loaded. A full restart shuts everything down and starts fresh. If your computer is slow, restart it before trying anything else—it solves the problem in 20 percent of cases.
Update your operating system and drivers
Microsoft and Apple release updates that patch security holes, fix bugs, and improve performance. Outdated drivers—the software that controls your graphics card, network adapter, and other hardware—can cause slowdowns and crashes. Check for updates monthly.
On Windows, go to Settings, select Update & Security, then Windows Update. Click Check for updates. On Mac, go to System Settings, select General, then Software Update. Install any updates available and restart your computer. For drivers, Windows Update usually handles them automatically, but you can also visit the manufacturer's website (Dell, HP, Nvidia, Intel) and read the latest drivers for your specific model.
Frequently Asked Questions
Is it safe to delete files from the Downloads folder?
Yes. The Downloads folder is meant to be temporary storage for installers and documents you read from the internet. Once you have installed a program or saved a document elsewhere, the installer is safe to delete. Review the folder first to make sure you are not deleting something you need, but most Downloads folders are full of old files you will never use again.
What if I disable a startup program and something stops working?
Re-enable it. Open Task Manager or Activity Monitor again, find the program in the Startup or Login Items list, and turn it back on. Restart your computer. There is no penalty for enabling and disabling programs—you can experiment without risk.
How often should I run a malware scan?
Windows Defender runs automatically in the background, so you do not need to do anything. If you want to run a manual full scan, once a month is reasonable. If your computer is running very slowly or behaving strangely, run a scan when ready—malware is a common cause.
Can I upgrade my hard drive or add more memory myself?
On many desktop computers, yes. Adding RAM (memory) is usually straightforward: you open the case, locate the memory slots, and insert new sticks. Replacing a hard drive with a solid-state drive (SSD) is also doable on most desktops and some laptops. However, if you are not comfortable opening your computer, a technician can do it for $50 to $150 in labor. Consult your computer's manual or manufacturer website first to confirm what upgrades are possible for your specific model.
Should I use a cleaning utility or optimization software?
Most commercial "PC cleaner" or "optimizer" software is unnecessary. Windows and Mac have built-in tools that do the same job for free: Disk Cleanup (Windows), Storage Management (Mac), Task Manager, and Activity Monitor. Avoid paid utilities that promise to "speed up your computer by 300 percent"—those claims are marketing, not reality. Stick with the free tools built into your operating system.