Why wont WMP play DVDs?

I have a new laptop, a Fujitsu Siemens Esprimo Mobile V5535 running Windows Vista Basic. When I try to play a DVD, it goes to launch it in WMP then comes up with an error message saying it can't play the DVD, maybe I need to adjust my resolution settings to a lower setting. I tried this and I still get the same error. It plays CDs fine. I've downloaded another player from online and that plays DVDs ok. Is there anything I can do to get WMP to work or should I just give up?!