Getting Error Message when playing MP4 Files

So today when I log into my computer and then go to my videos library and click play all, I have over 600 video files I get the error message saying No playable file is found and then I do a system restore and then it works fine, what can I do so this will never happen to me again, my default program for playing videos is Windows Media Player and I am running Windows 7 Professional

Hi there

1) BACKUP Video files (and other USER DATA files - music/photos/documents etc) to SEPARATE partition(s) / disk(s) -- away from the OS -- that way if you restore / upgrade your OS you don't lose the data.

2) for playing mp4 etc why not use VLC (free) -- almost ANYTHING is better than Windows media player.

(If you keep your user data AWAY from the OS you only need around 40 GB for your windows "C" partition - quicker to backup and restore !!).

Cheers
jimbo