Most videos don't work on my computer. Most will say that I need to download Flash Player. Even after downloading and installing it, the video still doesn't work and I get the same message about downloading Flash Player.
If after downloadin and installing the Flash Player plug-in you receive the same message, it means that the videos you are trying to watch are hosted on a scam website. By now, you must have infected your computer with malware. Download and run a copy of AdwCleaner and scan your computer. At the end of the operation, run Combofix to perform automatic cleaning.