No Disk error usually appears when DVD player is not reading the disc. The laser lens is probably dirty and need to be cleaned.
The lens can be cleaned with a clothe moistened with alcohol. A cotton bud will do also. Just gently wipe it on the lens.
You probably would have to open the cover of the DVD player. Inside this unit you will find the mechanical loading disc tray. The one where disc is loaded that moves in and out when ejecting or inserting the disk. In the middle of the mechanical loading you will find a spindle motor and beside this is a small glass illuminating red when the unit is on. This is the lens. Clean it with a cotton bud moistened with alcohol.
You may also need to check the ribbon wire. It is important, cause it's the one that connects the lens and the CPU. Replace it with a new one if possible.
It is good to check then secure also the connectors from the board and to the mechanical system.
These are the things to consider when a " No Disk " error appear on your DVD player when you load a playing DVD disk.