Reinstall/update the CD/DVD unit driver from the Device Manager, and restart the computer. If it doesn't work, try the following to attempt restoring the drive to normal.
1. Open the drive and clean the laser lens with a soft clean cloth moistened with few drops of alcohol
2. Lubricate the laser pick up assembly rails with a very small amount of light grease lubricant (vaseline or similar, and apply it carefully to prevent contaminating the drive)
The laser is very sensitive to dust, a very small amount can block the laser beam from reading the CD... and if the rail lube has dryed out, the laser pickup assembly will not slide as freely as necessary to efficiently read the CD. And if both laser lens and laser pickup rails need attention, reading CDs becomes a problem. So, try servicing the drive as suggested and reinstall the driver... If no improvement, the drive is probably dead.