Here is another test. Download your friend's video, the one that plays fine, to your external harddrive and see how it goes.
I had trouble playing videos from my portable (USB-powered) Western Digital 1 TB hard drive. The video stops and stutters. When I copied the video to my hard drive though it played fine. So I guess that eliminates the possibilities that there's something wrong with (a)the video or (b)the PC that's playing it?
Next I tried a similar thing with my portable Western Digital 500GB hard drive. I didn't actually use the same video but a similar one and the video played fine from the hard drive. I didn't have to copy it to my internal HD.
So does someone have any idea why this might be and how I can fix it? I'd like to use my 1TB play movies without having to copy them to internal hard drive every time.
Another thing: my 1TB HD (which I'm having problem with) has NTFS format while my 500GB one has FAT32 - if that helps. I've posted this on the storage forum also.