Hi, either try the players below or you may try converting your videos to a smaller size 8 gig is huge for a video to me. First make sure you video acceleration is set to full, if it isnt then that could be the problem,
http://pptfaq.com/FAQ00129.htm (Here is a guide covering windows 98 through vista hardware acceleration, scroll down til you see vista.)
Honestly I think any video that's 8 gig would cutout in any player. That is very large for a video file, most older harddrives were 10-40 gig by themselves. I recently answerered a question about hd videos lagging for someone and it turns out my answer was chosen as best, he said kmplayer was the only one that didnt cut out as much. However i'm not sure if kmplayer works on 64-bit,
Since you've already tried vlc and media player classic. You should try gom player, kmplayer or mplayer for windows. Mplayer for windows is similar to vlc because it has it's own codecs.
http://mulder.dummwiedeutsch.de/home/?page=projects (This is the best front for mplayer I know of. Mplayer has many different fronts such as smplayer and kmplayer. This one includes smplayer an mpui original mplayer.) You may wanna try it. It can be uninstalled normally. It works on 64-bit.
http://www.gomlab.com/eng/GMP_Introduction.html (Official site for gom player. Unlike kmplayer, this can be uninstalled normally without problems) It does support 64-bit.
http://download.pandora.tv/?mode=kmp&tab=1 (Official site for kmplayer. If you install this player and do not like it, please read the IMPORTANT information below about how to uninstall it properly.) This might not support 64-bit. It is not related to mplayer, there are 2 different kmplayers people get mixed up. This one is independent and made by koreans.
http://www.kmplayer.com/forums/ (Official kmplayer help and skin forums. You can probably find a newer version of kmplayer here.) If you can find a newer version here it may support 64-bit.
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If you go with kmplayer and do not like it. Here is how to PROPERLY UNINSTALL it. Failure to uninstall it this way will leave files associated with it after it's gone.,
Open kmplayer. Right click on it and click on "options", in the popout list click on preferances. To the left at bottom click on association/capture. At top click on second tab over "association". In association click the none button. Then click "apply to system". Close it out and close the player. Now you can simply uninstall it. You can manage file associations here also.
http://www.anvsoft.com/any-video-converter-free.html (Official site for any video converter free version, a very popular video converter.) Your last option.
I hope this helps you out. If not I post additional details and I will try to help you further. See link below to manage file associations between players.