PC running slow all of a sudden? Start with what changed

There is a difference between a PC that has been getting gradually slower for two years and one that was fine last month. The first is accumulation. The second has a cause with a date attached, and finding that date is faster than working through a general checklist.

Six things change quietly enough that nobody connects them to the slowdown.

1. Something new is running at startup

Installed anything in the last few weeks? Plenty of applications add a background helper or an updater that now starts with the machine and never stops.

Task Manager (Ctrl + Shift + Esc) → Startup apps, sorted by impact. Anything you do not remember agreeing to is a candidate.

2. A process is stuck

Background jobs occasionally fail in a way that leaves them consuming a core indefinitely — search indexing, a sync client, an update service, a crash reporter.

Task Manager → Processes, sorted by CPU, while the machine is slow. One thing sitting at the top with nothing running is your answer. A restart clears it; if it comes back within a day, the application needs attention.

3. The drive quietly filled up

This one has a threshold, which is why it feels sudden. A drive at 60% full behaves normally. The same drive at 95% is slow at everything, because Windows has no room for temporary files, updates and the page file.

Settings → System → Storage. Get back above 15% free and the machine recovers immediately.

4. Your browser session got heavy

Sudden in the sense that it builds up over a week you were not paying attention. A browser left open through a busy project accumulates tabs, each holding its own memory, and once RAM fills the whole machine starts swapping to disk.

The tell is that individual programs feel fine but switching between them freezes for several seconds. If that is what you have, releasing what those tabs hold fixes it in seconds without closing anything.

5. A recent update is still settling

After a major Windows update, the machine re-indexes and reoptimises in the background for a while. That is normal and it ends. If it has been more than a couple of days, stop blaming the update and keep looking.

6. The drive is failing

The one worth ruling out early, because it is the only item here with a deadline. Drives degrade rather than dying cleanly, and the early stage looks exactly like a slow computer — long boots, applications hanging, occasional freezes with heavy disk activity.

If Task Manager shows the disk at 100% active during ordinary work, check the drive's health and make sure your backups are current before doing anything else.

What about viruses?

Possible, and less common than the six above. Run a full scan with the security software already built into Windows — once. If it comes back clean, the cause is on the list above, and additional scanners will not change that.

Still nothing?

Then it is not sudden after all, and it is worth identifying which resource is short — memory, CPU, disk or heat — before changing anything else. Two minutes of watching beats an afternoon of guessing.