Restart or Shut Down? Your PC May Not Have Rebooted

You switch your PC off every night, and it may not have genuinely restarted in weeks. One line tells you when it last really booted.

That gap is not a fault. It is a Windows feature, and it explains why restarting cures things that switching off overnight never does.

I checked mine while writing this and found something the setting on its own does not tell you.

One line names the last real boot

Start here, because the number will probably surprise you. Open PowerShell and run:

Get-CimInstance Win32_OperatingSystem | Select-Object LastBootUpTime

Ours, and read on the desktop this was written on. It came back with a date ten days earlier, on a machine that gets switched off most evenings. Shutting down and starting again had not produced a real boot in over a week.

That is the whole article in one number. The line runs as an ordinary user and writes nothing, a plain read that answers in five seconds.

What Windows is doing instead

Documented by Microsoft in the driver reference rather than the help pages, the three startup modes are "Cold (traditional)", "Wake-from-hibernation", and "Fast (combines first two, introduced in Windows 8)".

The startup modes page says: "a fast startup simply loads the hibernation file (Hiberfil.sys) into memory."

Microsoft describes the shutdown half too: "Windows saves the kernel memory image (including the loaded kernel-mode drivers) in Hiberfil.sys and shuts down the computer." So your shutdown saves the running kernel and puts it back.

Drivers are not re-detected, services are not re-created, and anything wedged inside them stays wedged.

Which is why restart and shut down are different

The practical consequence contradicts what everybody assumes. A restart is a full cycle. Fast startup does not apply to it, and the kernel and every driver are built fresh.

A shutdown followed by pressing the power button is not. It reloads yesterday's kernel image, quickly. The same state carries forward. That is why "have you restarted it" beats "have you switched it off".

Not the same instruction, and the second is weaker. Holding Shift while you click Shut down forces a full one. The same mechanism explains a Bluetooth radio that vanishes and comes back.

Ours: the switch said on and the file was missing

Ours, and read on the same desktop. The registry flag for fast startup was set to 1, meaning enabled, and hiberfil.sys did not exist on the drive at all. Check both, not just the switch:

Test-Path C:\hiberfil.sys

A False there means the setting is decoration. Fast startup cannot work without that file, and Microsoft's own description is that it loads Hiberfil.sys into memory, so with no file there is nothing to load.

The setting can read as on while doing nothing. Turning hibernation off to reclaim disk space removes the file, and the switch stays behind, pointing at nothing. Worth knowing before you spend an evening on something already inert.

Where the setting lives

If yours is genuinely working and you want it off, open Control Panel > Power Options > Choose what the power buttons do. Unlock the greyed section, then clear Turn on fast startup. Ours: leave it on unless you have a reason.

It saves real seconds on a mechanical drive, and few enough on a modern SSD that the trade is close. The reason to turn it off is dual boot. A Windows partition left in that state can be corrupted by another operating system writing to it.

The other reason is hardware that misbehaves at power on. A keyboard that is dead cold and fine after a restart is the classic case.

When a real shutdown is the right move

Being specific, because "restart it" gets said far too loosely. Before opening the case, always: full shutdown, then unplug, then hold the power button for fifteen seconds to drain the board.

After installing a driver too, because the old one is only truly gone on a cold start. And before a BIOS or firmware update. Those expect a clean state and a saved kernel image is not one.

Works after a restart, breaks again after a night off? You have found fast startup. Not a hardware fault.

What a restart will not fix

Honest, because restarting is what people tell you when they cannot help. It will not fix a drive that is full. That takes actual space, and there is an order to finding it.

It will not fix failing hardware. A restart that helps for an hour and then does not is a symptom, not a solution. Nor something that starts with Windows. A problem returning within a minute of every boot loads with the machine.

The habit worth having

Short, and it costs you nothing. Restart once a week rather than shutting down every night, and one real boot a week clears more than seven fast startups do. Use the Start menu Restart, not the power button.

If the Start menu offers no Restart at all, typing shutdown /r still works.

Restart is the one that always does a full cycle, whatever the setting says. Ours: I run that line whenever a machine is behaving oddly. A boot time from three weeks ago explains a lot of complaints before anything else gets touched.

Status: measured on this desktop 24 August 2026, Windows 11. The three startup modes, the line that a fast startup loads Hiberfil.sys into memory, and the description of Windows saving the kernel image into that file all come from Microsoft's driver reference. The last boot date, the enabled flag and the absent hiberfil.sys were read right here.

How do I check when my PC last restarted?

Run Get-CimInstance Win32_OperatingSystem and look at LastBootUpTime in PowerShell. You do not need to be an administrator, and nothing on the machine is touched. Switch off nightly and the date is often days old. Fast startup is why.

Is restart the same as shut down and start again?

No. Microsoft documents fast startup as saving the kernel memory image to Hiberfil.sys at shutdown and loading it back at power on.

A restart does a full cycle instead, which is why restarting fixes things that switching off overnight does not.

Should I turn off fast startup in Windows?

Usually not. Turn it off for two reasons only. If you dual boot, because another system writing to a Windows partition left in that state can corrupt it. Or if hardware misbehaves at cold power on. Otherwise it costs you nothing.

Why is fast startup on but not working?

Check whether hiberfil.sys exists. Fast startup loads that file. Turn hibernation off to reclaim disk space and the file goes with it. The setting then does nothing. On the machine tested here, the flag read enabled and the file was absent.

Does Shift plus Shut down do anything different?

Yes. It skips the saved kernel image and performs a full shutdown instead, the same as a restart does. That is why it appears in troubleshooting advice for hardware that misbehaves at power on.

It can also leave you watching Getting Windows ready for a while, since pending update work runs then. The drive light tells you whether to wait.

The Short Version

• LastBootUpTime names the last real boot, and it is often older than you expect.
• Microsoft documents fast startup as loading Hiberfil.sys into memory at power on.
• Shutdown saves the running kernel. Restart builds a fresh one.
• So restart and shut down are genuinely different instructions.
• Holding Shift while clicking Shut down forces a full one.
• The flag can read enabled while hiberfil.sys does not exist, which makes it inert.
• Turn it off for dual boot, or for hardware that misbehaves at cold power on.
• Restarting once a week beats shutting down every night.

Where to Next

If the machine wakes itself in the night rather than refusing to shut down, something has permission to do that. Six devices were allowed to on the PC measured here.

If your PC is slow to start rather than slow to shut down, the same setting is behind a lot of it. Fast Startup changes what you are even measuring.

And if a machine you connect to remotely keeps dropping, it is usually asleep rather than broken. Remote Desktop failures get blamed on the network far too often.

Run the one line and look at your last boot time. Older than a few days? You have just learned something about how your machine really shuts down.

Then check whether hiberfil.sys exists. A setting that reads enabled with no file behind it is doing nothing at all.

Next time anything misbehaves, restart rather than shutting down. They are different operations and only one of them rebuilds the drivers.

And if your last boot time comes back weeks old on a machine you switch off nightly, tell me the number in the comments. I would like to know how far this goes.