Mac Pro keeps ejecting Windows 7 disc on boot!

[digiegg]

I don't know why but it keeps ejecting it on boot.
It installed fine on my Macbook Pro but Mac Pro keeps ejecting it... =(
Is there a step I'm missing out on?
This isn't bootcamped. I've had Vista 64 on the harddrive by itself before and now I'm trying put 7 on it. I insert the disc, reboot the computer, and it just keeps rejecting it. I really want to do a fresh install on this computer. What do I do?

 

[Markov]

Try reburning it. My macbook pro didn't like it either, but it never spit it out. I had to slipstream a patch to make my mbp understand how to boot from it.