my macbook pro reject disc/dvd what might b the problem

In such cases the first thing to do is to clean the drive. Many times, drives that seem to have failed only have a dirty lens. In that case they can be restored to full function with a simple cleaning.

Get a drive cleaning disk. They are available from home electronics stores, computer shops, and office superstores that sell computer equipment. The type I use is the "dry" kind s othere is no danger of moisture getting inside the computer. HEre are some Amazon offerings:

https://www.amazon.com/s?ie=UTF8&page=1&rh=n%3A172282%2Ck%3Acd%20dvd%20drive%20c leaner

Again, go for "dry."