Dvd/cd rom not working

Hello,
i have been trying to sort my laptop out for days now and i just seem to do i have reinstalled windows 7 a few times now and im still getting the same problems, in my device manager i have no problems with it finding the dvd/cd rom my problem is that my laptop will not read any disk when i put a disk in the drive it tries to loads and it lights up but then it will just open again and say please insert a disk. i have a acer aspire 5551 please some one help me i bet it is something really simple 2 lol