whenever i try to play a song or video ... this message pops up...

Windows Media Player cannot play the file. The Player might not support the file type or might not support the codec that was used to compress the file.

This is most likely a codec issue.

I recommend using VLC media player (it can play anything). Best part is it's free, open source and completely free of spyware. It is also the most popular player out there.

VLC media player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, ...) as well as DVDs, VCDs, and various streaming protocols.

If you also want free codecs, the K-Lite Codec Pack should be able to play 99% of all the movies that you download from the internet.