Video will not let me fast forward?

I took a video with my webcam. And my computer unexpectedly shut down while recording and it saves to my external hard drive. and when i turned my computer back on, the video will not let me skip through sections. I tried copying the file to a new folder on my computers hard drive, but it has the same problem. So, how can I edit it? or get it to let me skip through sections while playing the movie? or even just re-record the movie and make a new file?