Try these checks in order:
- Connect the reader directly to the PC
- Do not use a USB hub or dock.
- If the PC has more than one USB port, try a different port.
- If it is a USB-C reader, make sure it is connected to a USB-C port that supports the device features.
- Check power-related issues
- If the reader has an external power option, connect it.
- Plug the PC into external power instead of running on battery.
- Disconnect other unused USB devices, because the PC might not be providing enough power to the reader.
- Check whether Windows detects the device
- Select Start, type device manager, and open Device Manager.
- Look for the card reader or any device with a yellow exclamation mark.
- Right-click the device, select Properties, and check Device status for an error code.
- If Windows shows “USB device not recognized”
- In Device Manager, note the error code shown for the device.
- Follow the troubleshooting for that Device Manager error code.
- Check whether the card appears as a disk
- Press Windows + R, type diskmgmt.msc, and press Enter.
- Insert the card and watch whether it appears briefly, disappears, shows No Media, Unallocated, or has no drive letter.
- If it stays visible but has no drive letter, right-click the volume, select Change Drive Letter and Paths, and assign a letter.
- If the reader appears briefly and then disconnects
- This can indicate a USB power or compatibility problem.
- Test the reader on another USB port or another PC.
- If it fails on multiple PCs, the reader itself may be faulty.
- If the issue started after sleep/resume on older Windows versions
- On Windows 8.1, Windows RT 8.1, or Windows Server 2012 R2, there is a known issue where SD card insertion may not be detected after resume from sleep when using a USB SD card reader.
If the device is not listed in Device Manager at all after trying different ports and power checks, test the reader on another computer. If it still does not power on or connect, replacement of the reader is the likely fix.