Maybe the dongle is frozen. To unfreeze it, unplug it from the computer and plug it back in after a minute or two.
Maybe your device's bluetooth issue can be resolved easily by the manufacturer's customer support team. All you need to do is to call them and follow their instructions. Also, most of the manufacturers have a troubleshooting page on their websites, which can help you fix your device's bluetooth feature by yourself.
Maybe the USB port in which you plugged in the dongle doesn't work. Try plugging in the dongle in a different port.
Note: If you plugged in the dongle in a USB hub, plug the dongle directly in the computer's USB port.
Maybe the USB port where you tried to plug in the dongle is clogged with dust. Clean the ports with a tiny toothpick, or a vacuum cleaner with its suction power set to minimum. Also, you can apply some isopropyl alcohol on a cotton bud and clean the ports with it.
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