NAD 521i Troubleshooting

I've had a 521i for about 2.5 years, and it suddenly stopped recognizing CDs, both burned and normal. When I push the close button, it brings the CD in, then makes a whirring noise for about 3-4 seconds, then just continues to blink without making the noise. When I re-open it, the CD doesn't appear to have moved.

Would anyone know what this problem is caused by, or how to fix it? I used compressed air and a cleaning CD on it, and it worked again for a few days, then just went kaput again.

Any advice would be greatly appreciated.