If plugging it into a different USB port doesn't work, try using a different USB cable. Your driver may also not be correctly installed; check this link for the correct driver. If it doesn't connect to your computer but connects to another computer, it's possible that the USB port in your computer has lost connection with the computer's motherboard; if so, you'll need to open up your computer and re-attach the internal USB cable with the motherboard. Search iFixit for instructions on how to do this with your computer. You can check the troubleshooting guide for your device for more information.

Yes, you can. If you'd like to make the keyboard more quiet without replacing the keyboard's switches, you can follow this guide to install O-rings on your keyboard. However, if you'd like to replace the switches themselves, you can follow this guide. If you'd like to see more information about the device, you can look at its troubleshooting page.

Yes, there is! If the keyboard works as expected, and the only issue is that the light under the key cap isn't turning on, you can replace the LED under the key cap by following this guide. If there are issues with the keyboard other than the light, you can look at the troubleshooting guide.