Bluetooth Device Not Found, Why Windows Can't See It
Windows saying it cannot find a Bluetooth device almost always means the device is not actually advertising itself yet, or another device grabbed the connection first. Bluetooth devices only show up in the Add device list while they are in pairing mode, so the fix is usually on the device, not the PC.
Fix it, in order
Put the device in pairing mode properly. Most headphones and speakers need a button held for several seconds until a light flashes, and opening the case or turning the device on is not the same thing. Check the device manual for the exact gesture, and watch for the flashing light that confirms pairing mode.
Move the device close to the PC. Keep it within a few feet during pairing, with a clear line of sight if possible. Walls, a metal desk, and other electronics in between weaken the signal enough that discovery fails.
Disconnect the device from anything else first. A Bluetooth device that is already connected to a phone or tablet will not advertise for pairing. Turn Bluetooth off on the nearby phone, or disconnect the device there, then try again.
Restart Bluetooth on the PC. Press Win + A, turn the Bluetooth tile off, wait ten seconds, and turn it back on. Then open Settings, Bluetooth and devices, Add device, Bluetooth, and start the scan before putting the device in pairing mode.
Set Bluetooth discovery to Advanced. In Settings, Bluetooth and devices, Devices, Device settings, change Bluetooth devices discovery to Advanced. The default setting can hide some devices from the Add device list.
Restart the Bluetooth Support Service. Press Win + R, type services.msc, and press Enter. Right-click Bluetooth Support Service and select Restart. This service handles discovery and pairing, and when it has stopped Windows cannot find new devices even though the Bluetooth switch looks fine.
Remove any stale entry and pair fresh. If the device appears in Settings, Bluetooth and devices, Devices, select the three dots next to it, choose Remove device, confirm, and pair again from scratch.
Do not buy a driver updater to fix discovery. Bluetooth discovery is handled by Windows and the device's pairing mode, and third-party driver tools cannot make a device advertise itself.
If it still happens
If the device pairs fine with a phone but never appears on the PC, the PC side is the problem. Update the Bluetooth adapter driver in Device Manager, and try a USB Bluetooth adapter to test whether the built-in radio is at fault. If the device appears in the list but pairing fails every time, the page on Bluetooth that will not pair covers the next steps.
Common questions
Why does my device show up on my phone but not my PC? The device is probably still connected to the phone, which stops it advertising for new pairings. Turn Bluetooth off on the phone for a minute and try the PC scan again.
The Add device window spins forever and finds nothing. What now? Restart the Bluetooth Support Service and set discovery to Advanced. If the scan still finds nothing, the adapter driver is the next suspect, so update or reinstall it in Device Manager.
How close does the device need to be? Within a few feet for the first pairing. Once paired, most Bluetooth devices work across a room, but discovery is much more sensitive to distance and interference than a connected link.