If you right click on something, say a Youtube video, and click settings, is hardware acceleration checked? Maybe it got unchecked somehow.
Also, I know you've said you've uninstalled/reinstalled flash, but just to make sure did you use /Applications/Utilities/Adobe Flash Player Install Manager/, uninstall, and then download and reinstall the latest version of flash or something else?
Also, I know you've said you've uninstalled/reinstalled flash, but just to make sure did you use /Applications/Utilities/Adobe Flash Player Install Manager/, uninstall, and then download and reinstall the latest version of flash or something else?