My Mac OSX 10.7.5 won't play DVDs anymore.

I don't know if I have done something, or the computer is just getting old, but our Mac OSX 10.7.5 will not play DVDs anymore. Sometimes it just whirrs and makes a noise, never playing. Other times it just spits it back out. Is there any way to fix this problem so I can play DVDs again? Thank you.