Ok i found this one on the internet and i decide to try it.
And it worked!!!!
Step 1: When you click play on a Megavideo video, click pause and allow the video to buffer all the way to 100%.
Step 2: Once the video is done buffering, go to your menu bar on your browser, and click on File -> Work Offline.
Step 3: Watch video.
Step 4: Unclick the "work offline" button to reload another video. You can have a megavideo marathon with this method.
Try to use firefox it works better and clear all of ur cookies
enjoy~~~