All of a sudden, flash videos won't start until all of the movie is loaded. Affects every flash movie youtube, brake.com, my own videos.. I have Vista SP1 and I have tried uninstalling / reinstalling flash player.
If you have uninstall flash through the "add/remove programs", it might not be totally uninstalled.
Try the official Flash Uninstaller here, remember to reboot windows before reinstalling: http://www.adobe.com/support/flashplayer/downloads.html#uninstaller