If you download videos from YouTube, you have to check with the YT downloader you're using. For good quality video, it has to be at least one gigabyte per hour of video. For HD video, it is double that.
So, for the video you downloaded - what is the size, and what is the playtime? Right-click in file name from Windows Explorer, Properties, go to Details tab - what is listed there as resolution, bit rate, etc?
The bottom line - if the downloaded video is of bad quality, no player will help. Your laptop is more than good to handle HD videos.