Why can't I watch DVDs on my laptop (WIN10) even though I have windows media player?
Take VLC, it will work.
http://www.videolan.org
Maybe you do not have a DVD drive or your screen is broken.
A few more details would be pretty good.
If I'm not mistaken, the Windows Media Player in Windows 10 is only a much slimmed down version compared to the WMP in earlier versions of Windows.
Therefore, get a non-functional media player software (freeware) from a third-party provider.