This has never happened to me until now, and I don't know why (which is why I'm on the forums). Pictured below is how it looks in After Effects.
Both the selection thumbnail and the video is half blacked out. However, the picture below shows the thumbnail for the video outside AE and
it's perfectly fine.
There was a thread on this problem just two days ago. A search for black video would have given you the thread. It is the first one.
This is a problem acknowledged by Microsoft. It's their fault. http://support.microsoft.com/kb/2803821 You'll have to either use a different codec or wait for Microsoft to solve the problem with an update.
WMV is a terrible file container anyway. While After Effects has made amazing leaps and bounds in different codec support over the years, you will always have the most pain-free production pipeline if you use tried-and-true intermediate filetypes like Quicktime (Animation, PNG and ProRes codecs), uncompressed avi etc.