Pin down what 'slow' actually means
Slow is a vague complaint, and different kinds of slow have different causes. A computer that takes five minutes to start points to a different problem from one that freezes when Teams and Excel are open together, or one where only the accounting system crawls. Ask the person exactly what is slow, when it started, and whether it happens everywhere or only in one application or one location.
Then check whether others are affected. If everyone in the office is complaining about the same shared drive or web app at the same time, the issue is almost certainly the network, the internet connection or the service itself, not the individual computers. Replacing laptops in that situation wastes money and leaves the real fault in place.
Memory and too many things running
Open Task Manager with Ctrl, Shift and Esc and look at the Memory figure on the Performance tab. If it sits above about 85 per cent during normal work, the computer is running short and constantly shuffling data to disk. Modern browsers with dozens of tabs, Teams, Outlook and a couple of large spreadsheets can easily consume 8GB, which is why older laptops with that amount struggle.
Check the Startup apps list in Task Manager or Settings too. Printer utilities, update checkers, chat apps and vendor tools pile up over the years and all start when the computer boots. Disabling the ones nobody needs shortens startup and frees memory. On desktops and some laptops, adding memory is a cheap and effective fix; on many thin laptops it is soldered in and the only options are reducing the load or replacing the machine.
Storage: full drives and old hard disks
A drive that is more than about 90 per cent full slows Windows noticeably and blocks updates from installing. Clear the Downloads folder, empty the recycle bin, run Storage Sense in Settings, and use OneDrive's files on demand so cloud files don't all sit locally. Large local Outlook data files and old installers are frequent culprits.
If the computer still has a mechanical hard drive rather than a solid-state drive, that alone can explain a slow start and long waits opening files. You can usually tell by the model's age or by looking at the drive type under the Performance tab. Replacing a hard drive with an SSD is often the single most dramatic improvement you can make to an older desktop.
Updates, security tools and background tasks
A machine with weeks of pending updates may download and install them in the background while someone is trying to work, and some updates only finish after a restart that keeps being postponed. Restart the computer properly, let updates complete, and set a regular restart schedule. Many office computers that feel sluggish have simply not been restarted in a month.
Two security products running at the same time can slow a computer badly as they scan each other's activity. Make sure there's only one endpoint protection tool installed. Backup software, search indexing and cloud sync can also briefly use a lot of resources, especially after a big change such as moving thousands of files into OneDrive.
When it really is the network or a service
If a cloud application is slow but other websites are fine, check the provider's status page and ask whether colleagues see the same thing. If everything online is slow, run a speed test on a wired connection and compare it to Wi-Fi. Weak Wi-Fi, an overloaded router or an old switch can make a fast fibre connection feel like dial-up at the desk.
Files opened from an on-premises server or NAS over the network depend on that device and the cabling between. A failing drive in the server, a network port running at 100Mbps instead of a gigabit, or someone syncing a huge folder can make every computer seem slow. Those problems need fixing at the source.
Hardware warning signs and when to replace
Fans roaring during simple tasks, a hot chassis, sudden shutdowns or performance that drops when the laptop is unplugged suggest overheating or a worn battery. Dust buildup inside desktops and laptops reduces cooling and throttles the processor. Disk health warnings, repeated crashes and blue screens point to failing hardware that needs attention before it takes data with it.
If a computer is more than five years old, has a processor that can't run Windows 11, or has soldered memory that is clearly not enough, cleaning and tweaking will only get you so far. At that point it is usually cheaper to replace it than keep paying for time spent waiting and troubleshooting. A quick check of the whole fleet shows which machines are worth fixing and which should be on the replacement list.
In short
- Find out exactly what is slow and whether others are affected.
- Check memory use and trim startup apps in Task Manager.
- Keep drives below about 90 per cent full and replace old hard disks with SSDs.
- Restart regularly so updates finish, and run only one security product.
- Replace machines that can't run Windows 11 or have too little memory.