Go to the media generators tab and choose one of the solid colors you want (Normally people use white or black to create the strobe effect). Then once you put it in the time line shorten it's duration to about .003 or what ever duration you want/need for it, and put it in the layer above your main footage, and place it at the part in the video where you want it. You can also change is opacity by adjusting the crossfade level if you don't want it to be a real hard flash.
You can play around with it and preview it until it looks perfect in your time line to your liking.
There is another way too which is to use the Video fx & transitions, but that takes up more of your PC's resources and it's alot more work to do with it to get the proper duration out of it. Plus doesn't always look the same.
Hope that helps!
