My Mac Mini doesn't wants CD I had a Mac mini. Then the HD broke. So I took an HD from an old Windows notebook. I moved this HD from the Windows notebook to the Mac mini. Now Mac mini correctly starts with Windows XP (what a mess). 

So what I want now, is to replace Windows XP with an OS X, but as soon I insert the original Mac mini install disk, my device will spit it out. The same DVD is read on the other Windows computer. Why? What happened? And above all: what can I do????
Your DVD drive is probably done.
It's usual so what you can do is


use external DVD drive or
find a friend with a Mac and restore you DVD to 8GB+ flash drive (partitioned as GUID) through Disk Utility or
buy the latest Mac OS X (check if your Mini support it though) and restore it to USB flash drive.
You can also install Mac OS X on your HDD while put it in external box and using another mac.


Use option key to boot from flash drive.