What are the reasons I cannot play Blu-Ray Discs on my computer with Windows 7? I heard it has something to do with codecs which Microsoft chose not to include. If I bought a Blu-Ray player and do not have the disc that came with it, what type of software can I use to watch Blu-Ray Discs?

Quite often commercial disc come packaged with the required codecs/players for the content.

The hardware DVD player must be a Blu-Ray player. Software can't fix it.