I'm assuming this is a laptop. The thing to try is to look on the bottom of the laptop and find the screw that holds the rom mounted to the laptop. Remove it. Then remove the rom and then reset it in the slot. It could be a simple conection problem........If you try removing the rom......and replacing it......you should do a restart on it so the laptop re installs it.
If your afraid to pull the rom.......You could remove the dvd......and give the door a good slam....not too hard.....
then restart the laptop.