If you have more than one computer–for instance, a desktop and a laptop–you may have encountered video files that run on one machine but not the other.
That’s probably because of a codec conflict. Videos are encoded in assorted formats, and if, say, your laptop doesn’t have the proper decoder for a particular format, you can’t watch the video. Suppose you downloaded an episode of the criminally underrated–and canceled–FX TV show Terriers using BitTorrent. (I’m not here to judge.) If that video was encoded with, say, DivX or MKV, your PC won’t play it without the right codec (short for “coder-decoder”). Install K-Lite Codec Pack Full, which has everything you need to play AVI, FLV, MKV, and other formats.
If you bought a movie or TV show from Amazon Video on Demand or iTunes, you can’t just copy the file from one machine to another and expect it to play. This isn’t a codec issue, but rather a matter of digital rights management. Amazon customers should consult the “Managing Your Video Library and Licenses” page; iTunes users can read “iTunes for Windows: How to copy purchases between computers.”
(For more solutions to perplexing PC problems, see “The 21 Greatest PC Mysteries–Solved!“)