It's also why we keep a backup of a working system or be ready to start over.
For now, try playing with VLC Player. Get it from ninite.com. Here's why.
http://www.howtogeek.com/201354/ninite-is-the-only-safe-place-to-get-windows-freeware/
Hi :\ I have a computer trouble, yet again... I don't know what to do, I've run the computer's scan disk, a defrag, disk cleanup, and no matter what Windows Media Player refuses to load any movies/videos I have, and the computer is running slower than ever. I have a Optiplex GX620 Computer Windows XP but I am not sure ... does anyone have suggestions on what to do when something like this could ever come up? I am completely stuck at this point :\ Malwarebytes Anti-Malware ran and found 101 threats and got rid of them but it's still doing this ... help please :\ Youtube still works for example on Firefox! I have no clue :\ thank you.

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