Mac mini won't read data cd anymore?

My mac mini (2008 I believe, running on snow leopard?, v 10.7.1) won’t recognize a data cd that it read just fine a couple of weeks ago. When I put it in, it spins for a few seconds, then spits it back out.
I actually had that cd in there for a few days, when a couple of days ago, the mini decided to spit it out on it’s own.
I tried restarting, looked at the cd/dvd preferences, but nothing.
Sorry if I got any technical wording wrong. I’m not a computer kind of girl. =P
Thanks in advance!