The Most Common Reasons Your Computer Slows Down

A slow PC usually comes from one of five things: too many programs running at startup, a hard drive that is nearly full, malware or viruses, outdated drivers, or a failing hard drive. The first step is to figure out which one is happening to yours, because the fix is different for each.

Start by opening Task Manager (press Ctrl+Shift+Esc on Windows, or Command+Space then type Activity Monitor on Mac). Look at the CPU and memory columns. If one program is using more than 50% of either, that program is your problem. If nothing stands out and memory is above 80%, your drive is too full or you have too many things running.

Key Takeaways

  • Task Manager on Windows and Activity Monitor on Mac show you which programs are using the most CPU and memory right now.
  • Startup programs that run automatically when you turn on your PC are often the biggest cause of slowness, and you can disable most of them.
  • A hard drive that is more than 80% full will slow down even a new computer, and clearing space is one of the fastest fixes.
  • Malware and viruses hide in the background and use your CPU and internet, so running a scan with Windows Defender or a dedicated tool is worth doing.
  • Drivers are the software that let Windows talk to your hardware; outdated drivers for your graphics card or chipset can cause lag and stuttering.

Disable Programs That Start Automatically

Every program you install asks to run when your PC starts up. After a year or two, you might have 20 or 30 things launching before you even open a browser. Each one uses memory and CPU, and they all run in the background even if you never use them.

On Windows, open Task Manager (Ctrl+Shift+Esc), then click the Startup tab. You will see a list of programs with an Impact column showing High, Medium, or Low. Right-click anything marked High that you do not use every day and select Disable. Common culprits are Adobe Reader, Spotify, Discord, and Slack. You can always launch them by hand when you need them.

On Mac, go to System Settings, then General, then Login Items. Remove anything you do not need to start automatically. The difference is often noticeable within a day.

Clear Space on Your Hard Drive

When your hard drive is more than 80% full, Windows and Mac both slow down because they need free space to write temporary files. Check how much space you have left by right-clicking your C: drive (Windows) or clicking the Apple menu and selecting About This Mac (Mac).

If you are above 80% full, start by emptying your Downloads folder and your Recycle Bin or Trash. Then look for large files: go to your Documents, Pictures, and Videos folders and delete anything you do not need. Videos and old backups take up the most space.

If you still need more room, uninstall programs you no longer use. On Windows, go to Settings > Apps > Apps and Features, find the program, and click Uninstall. On Mac, open Applications, drag unused programs to Trash, and empty Trash.

Run a Malware and Virus Scan

Malware and viruses run silently in the background, using your CPU and internet connection. They are harder to spot than a slow startup program because Task Manager might not show them clearly. The safest approach is to run a full scan with a tool designed to find them.

On Windows 10 and 11, Windows Defender is built in and free. Open Windows Security (search for it in the Start menu), click Virus and Threat Protection, then click Scan Options. Select Full Scan and let it run. This can take 30 minutes to an hour, so start it when you do not need your PC.

If you want a second opinion, Malwarebytes is a free tool that catches things Defender sometimes misses. read it, run a scan, and restart your PC. On Mac, Malwarebytes is also available and worth running even though Macs are less often targeted.

Update Your Drivers

Drivers are the software that let Windows talk to your graphics card, network adapter, and other hardware. Outdated drivers can cause stuttering, lag, and high CPU use. The most important ones to update are your graphics driver (Nvidia, AMD, or Intel) and your chipset driver.

On Windows, right-click the Start button and select Device Manager. Look for any device with a yellow warning triangle. Right-click it and select Update Driver. For graphics, visit Nvidia.com, AMD.com, or Intel.com directly and read the latest driver for your card.

On Mac, go to System Settings > General > Software Update and install any updates available. Mac handles driver updates through the operating system, so there is no separate step.

Check for a Failing Hard Drive

If your PC is slow even after disabling startup programs and clearing space, your hard drive itself might be failing. Hard drives wear out after five to ten years of use, and a failing drive will make everything slow because the computer has to wait longer to read and write files.

On Windows, search for Check Disk in the Start menu. Right-click it and select Run as Administrator. A window will appear asking if you want to schedule a check on your next restart. Click Yes. Your PC will restart and run a scan that checks the health of your drive. This takes 10 to 30 minutes depending on drive size.

On Mac, open Disk Utility (Applications > Utilities), select your drive, and click First Aid. This checks for errors and repairs them if possible. If either tool finds problems, back up your files when ready and consider replacing the drive.

Reduce Visual Effects and Background Activity

Windows and Mac both use animations and visual effects that look nice but use CPU and memory. On older PCs or laptops, turning these off can make a noticeable difference.

On Windows, right-click This PC or My Computer, select Properties, then click Advanced System Settings. Under Performance, click Settings. Select Adjust for Best Performance to turn off all animations, or select Custom and uncheck the ones you do not want. The biggest impact comes from turning off Animate Windows When Minimizing and Maximizing and Fade or Slide Menus Into View.

On Mac, go to System Settings > General > Appearance and uncheck Reduce Motion if it is checked. Then go to System Settings > General > Login Items and remove anything under Allow in the Login Items section.

Frequently Asked Questions

How do I know if my PC is slow because of a virus?

Viruses usually cause high CPU use even when you are not doing anything. Open Task Manager (Windows) or Activity Monitor (Mac) and look at the CPU column. If it is above 30% when you are idle, run a full malware scan. Viruses also cause unexpected pop-ups, strange browser behavior, and internet slowness.

Will adding more RAM make my PC faster?

Only if your memory is constantly above 80%. Open Task Manager or Activity Monitor and watch the memory column while you work. If it regularly hits 90% or higher, more RAM will help. If it stays below 70%, adding RAM will not fix your slowness — the problem is elsewhere.

Should I use a PC cleaner tool?

Most PC cleaner programs do not help much and some are scams. The built-in tools in Windows and Mac (Disk Cleanup, Storage Management) are safer and free. Stick to those and the steps above instead of downloading third-party cleaners.

Why is my laptop slow but my desktop is fast?

Laptops overheat more easily because they have less space for airflow. If your laptop fan is loud or the bottom is hot, shut it down and let it cool for 30 minutes. Dust buildup inside also blocks airflow. If you are comfortable opening it, use compressed air to blow dust out of the vents. Overheating causes the CPU to slow itself down to protect the hardware.

Can I speed up my PC without buying anything?

Yes. Disabling startup programs, clearing disk space, running a malware scan, and updating drivers are all free and often fix slowness completely. The only time you need to buy something is if your hard drive is failing or you genuinely need more RAM, and those are rare.