Why Does My PC Get Slower After Running for Several Hours?

CoffeeAmericano

My Windows PC works fine after a fresh boot, but after several hours of normal use, apps start taking longer to open and the system feels less responsive. A reboot fixes it temporarily. What should I check to find out whether the problem is caused by RAM usage, background processes, disk activity, or something else?

LeoF_225

CoffeeAmericano The fact that a reboot fixes it is useful, but it doesn't automatically mean "not enough RAM."

I'd start by looking at what changes over time.

Open Task Manager when the PC is still running normally, note CPU / Memory / Disk usage, then check again when it becomes slow. If memory usage keeps climbing for hours and doesn't come back down, I'd suspect a process with a memory leak or simply an application accumulating a lot of working data.

Also check Committed memory under the Performance > Memory section. Physical RAM isn't the whole story. Windows can use the page file when committed memory gets high, and heavy paging can make the whole system feel sluggish even if CPU usage isn't particularly high.

homebuilder77

LeoF_225 Yep. I'd make this even simpler before digging into anything complicated.

Next time it happens, don't reboot immediately.

1. Open Task Manager.

2. Sort Processes by Memory.

3. Then sort by CPU.

4. Then check Disk.

5. Look at the Performance tab and see whether Memory, Disk, or CPU is actually pinned.

Take a screenshot.

The important part is catching it while it's slow. Checking Task Manager five minutes after reboot usually tells you almost nothing.

I've seen people spend hours disabling Windows services when the actual culprit was Chrome, a sync client, or one badly behaved app that had been sitting open all day.

ThisMakesNoSense

homebuilder77 I'd be careful with the usual "RAM usage is high = memory leak" diagnosis.

Windows using a large percentage of RAM is not inherently a problem. Standby/cache memory is intentionally used to improve performance and can be reclaimed when applications need it.

If you're testing this properly, look at Available memory, Committed memory, and the individual process working sets, not just the percentage shown on the Task Manager graph.

And if the system becomes slow while Disk is at 100%, don't assume the disk itself is failing either. "100% active time" can happen with relatively low throughput if I/O requests have high latency.

BinaryEcho

ThisMakesNoSense Task Manager is basically your PC's crime scene camera.

Don't reboot the suspect and then complain that there is no evidence.

😂

Seriously though, the "reboot fixes everything" pattern is exactly why you want to catch the machine in the slow state. Otherwise you're testing a completely different system.

PleaseExplain

BinaryEcho So the first rule is basically:

Don't restart before checking what is actually happening.

I've definitely been guilty of doing exactly that.

LeoF_225

PleaseExplain One more thing I'd check is paging.

If physical memory is under pressure, Windows may move memory pages between RAM and the page file. That doesn't necessarily mean the page file is "bad." It's just much slower than keeping actively used data in RAM.

A useful clue is this combination:

RAM usage is high

Committed memory is close to the commit limit

Disk activity increases when opening/switching applications

The machine becomes responsive again after closing some applications

That points more toward memory pressure than a generic "Windows gets slower after running for a while."

LeoF_225

PleaseExplain One more thing I'd check is paging.

A useful clue is this combination:

RAM usage is high

Committed memory is close to the commit limit

Disk activity increases when opening/switching applications

The machine becomes responsive again after closing some applications

That points more toward memory pressure than a generic "Windows gets slower after running for a while."

homebuilder77

LeoF_225 For a real-world test, I'd also use Resource Monitor.

Task Manager is great for the quick overview, but Resource Monitor can show which processes are generating disk activity and what files they're touching.

If Disk is busy, check whether it's actually your browser, OneDrive/Dropbox, Windows Update, antivirus, search indexing, etc.

I've had machines that looked like "slow disk" problems where the SSD was perfectly healthy. Something in the background was just hammering it with I/O.

ThisMakesNoSense

homebuilder77 And don't overlook CPU frequency / thermal throttling.

If the slowdown happens after the machine has been under sustained load, compare CPU utilization with actual clock speed and temperatures.

For example, 20% CPU utilization doesn't tell you much if the processor is running at a severely reduced frequency.

That said, for a PC that becomes sluggish after several hours of ordinary desktop use, I'd investigate memory pressure and background activity before blaming thermals.

BinaryEcho

ThisMakesNoSense This is why "CPU is only at 20%" isn't the magic certificate of innocence people think it is.

Your CPU can be sitting there at low utilization while another component is screaming for help.

PC performance isn't a democracy where CPU gets all the votes.

PleaseExplain

BinaryEcho The part about checking clock speed is new to me.

I usually only look at CPU percentage and call it a day.

LeoF_225

PleaseExplain I'd also check whether the slowdown follows a specific application.

For example, if the PC gets progressively worse after leaving a browser, IDE, VM, game launcher, or sync application running for hours, close that application when the slowdown appears and see whether responsiveness immediately improves.

That's a much stronger clue than simply saying "Windows gets slower after 6 hours."

If closing one process makes everything responsive again, you've narrowed the problem considerably.

homebuilder77

LeoF_225 And if it happens consistently, use a simple A/B test.

Day 1: use the PC normally and leave your usual apps running.

Day 2: don't launch one of the suspects.

Day 3: repeat with another suspect.

You don't need to disable 30 services at once. Change one variable at a time.

Also check Event Viewer around the time the slowdown occurs. Look for recurring warnings/errors rather than treating every warning as a smoking gun.

ThisMakesNoSense

homebuilder77 +1 on changing one variable at a time.

I'd also avoid blindly following advice like "disable the page file" or "turn off Superfetch" because someone on a forum said it makes Windows faster.

Those can create a completely different problem while hiding the original symptom.

If you're troubleshooting performance, measure first and modify second.