You’ve probably seen the suggestion that Media Player is corrupted, or that the files that you are using through Media Player are corrupted. It is possible; some viruses out there can activate themselves when certain programs are loaded, causing resources to be heavily depleted amongst other damage to the computer. It could have been corrupted by accessing a file disguised as a file-type that Media Player can access (a virus disguised as an MP3 or AVI, for example). Usually, once a program is corrupted, the only way to repair it is to uninstall and re-install it.
The only way to fully protect yourself from this is to run a virus scan on every new file you download. Using your virus scanner to check one file doesn’t take more than a few seconds. It's tedious, yes, but far less stressful than having to go through the rigorous process of uninstalling and reinstalling a program all over again.
Hopefully these possible scenarios include the one under which your computer falls under. Remember: Don’t run a lot of other programs while Media Player is running, make sure you have the latest codecs, and always make sure the files you’re running are legitimate. If certain files are too demanding on your computer’s resources, don’t access them.