Bluetooth Won't Turn On, Fix the Missing or Greyed-Out Switch
When Bluetooth will not turn on, the switch is usually greyed out, missing from Quick Settings, or flips back off the moment you tap it. The cause is almost always the Bluetooth radio losing power state, its support service stopping, or a driver that failed to load, and the fixes below go from quickest to deepest.
Fix it, in order
Check Airplane mode and the hardware radio key. Press Win + A and make sure Airplane mode is off. Some laptops also have a function key or a physical switch that turns all radios off, and Bluetooth stays off while that is engaged.
Toggle Bluetooth in Settings, not just Quick Settings. Open Settings, then Bluetooth and devices, and try the switch there. If the switch is missing entirely, keep going, the problem is below the Settings app.
Do a full cold shutdown, not a restart. Hold Shift, select Start, then Power, then Shut down, and wait one minute after the PC turns off before starting it again. A normal shutdown or restart can preserve the hung power state of the Bluetooth chip, and Microsoft recommends this exact step for a missing Bluetooth toggle.
Restart the Bluetooth Support Service. Press Win + R, type services.msc, and press Enter. Find Bluetooth Support Service, right-click it, and select Restart. If it is stopped, select Start. Double-click it and make sure Startup type is not set to Disabled, Manual is the normal setting.
Check Device Manager for the adapter. Right-click Start and select Device Manager, then expand Bluetooth. If the adapter has a down arrow, right-click it and select Enable device. If it has a yellow warning triangle, note the error code in Properties, then right-click it and select Update driver.
Reinstall the Bluetooth driver. In Device Manager, right-click the adapter and select Uninstall device, then restart the PC so Windows reinstalls it. If Windows installs the same broken driver again, download the Bluetooth driver from the PC maker's support site for your exact model instead.
Check the firmware setting. On some laptops Bluetooth can be switched off in the BIOS or UEFI setup, often under Wireless or Advanced. If the adapter never appears in Device Manager at all, check there before assuming the hardware has failed.
A desktop PC with no built-in Bluetooth has no switch to fix. A USB Bluetooth adapter adds it, and Windows treats that adapter exactly like built-in Bluetooth.
If it still happens
If the toggle is still missing after a cold shutdown, a service restart, and a clean driver reinstall, open Device Manager, select View, then Show hidden devices, and look for a greyed-out Bluetooth adapter or an Unknown USB Device. A Code 43 or Code 45 on a hidden adapter points to the wireless card itself, and on many laptops the Bluetooth radio shares a card with Wi-Fi, so a card that needs reseating or replacing is the next step, not another driver.
Common questions
Why is the Bluetooth toggle greyed out? The adapter is present but Windows cannot start it, usually because the Bluetooth Support Service stopped, the driver failed, or the radio is locked by Airplane mode or a hardware key. The cold shutdown and the service restart clear the first two causes.
Does my PC even have Bluetooth? Open Device Manager and look for a Bluetooth category. If there is none, even with View, Show hidden devices turned on, the PC probably has no Bluetooth hardware, and a USB Bluetooth adapter is the fix.
Bluetooth worked yesterday and stopped after an update. What changed? Windows Update sometimes installs a generic Bluetooth driver over the maker's driver. Rolling the driver back in Device Manager, under Properties, Driver, Roll Back Driver, or installing the maker's driver, usually restores it.