There's nothing like a quick YouTube break to shake up the workday monotony, but nothing will stop the show faster than a stalled video stream or a crashing media player. Make these sites your first stops when your media player goes on strike.
YouTube Help Center
The service's own troubleshooting page is a bit too quick to recommend that you uninstall and then reinstall the Adobe Flash Player (cutesy instructional video, though). This may be the surest cure for all types of glitches, but I would begin with the simpler steps the site suggests, such as restarting your browser, accessing the page using another browser, and clearing your browser cache.
In fact, I recommend that you clear your browser cache first; doing so takes only a few clicks and can cure a range of page-loading woes. In Firefox, click Tools > Clear Private Data, uncheck all options except Cache, and click the Clear Private Data Now button. In Internet Explorer, click Tools > Delete Browsing History, and click the "Delete files" button next to Temporary Internet Files.
Adobe offers a Shockwave Player support FAQ site that has a page specific to Windows XP and others that describe various error messages, along with info on other troubleshooting topics. You'll find the latest version of the Flash Player on the Adobe Download Center. The company's Flash Support Center is intended for Flash developers.
Troubleshooting Windows Media Player 11
Microsoft's own troubleshooting page for the media player built into Windows has separate sections for Most Popular Questions, Self-Help Options, and Technical-Support Options, in addition to the standard FAQs on playing DVDs, ripping MP3s, and finding and installing codecs.
There's a separate WMP FAQ page for Windows Vista. In typical Microsoft fashion, there's yet another troubleshooting page that focuses on problems when using the player in XP. And just for good measure, a Knowledge Base article listing troubleshooting resources.
Apple iTunes for Windows
Apple provides separate pages for troubleshooting iTunes video playback on Windows Vista and Windows XP/2000. The company covers "unexpected quits, freezes, and launch issues" on this page for Vista and this page for XP.
Apple QuickTime for Windows
The QuickTime Troubleshooting site lets you tell at a glance whether Apple's media player is installed and functioning (you'll see the animated QuickTime logo in the bottom-right corner if it is).
The company's support site offers pages for curing problems when installing QuickTime for Windows, enabling Flash content in QuickTime movies, viewing streamed files behind a firewall, and diagnosing audio-playback problems (which applies to iTunes as well).