Diagnosing the fauty parts on dvd player is quite technical but i will suggest a diy solution that may help you on your problem.
Try cleaning the Lens of your DVD(It might be covered by dust thats why it can't read any disc) by a soft cotton bud. Be careful while doing these and try if it will work.
If the problem is still there then i've advice you to send it to repair shop to replace the faulty parts.

Thanks for using fixya.