The LCD screen isn’t showing up properly. Some of the bars that make up the digits are really faint. Is there a way to fix...

How can I determine whether or not a CD will be able to work with this device?

The light is probably broken. To solve this problem you will need to open the device and solder in a new one, or replace the LCD’s board entirely. See the Insignia NS-B4111 Troubleshooting page for more information.