Its been a while since i did any of that from what i remember its all about getting it set up in the drivers properly. One needs to be primary and the other secondary then you get options to extend or clone the screens. it could be that the two are clashing.
I looked up this video that runs through a W7 install and it would seem like both monitors should be connected at atart up which could also be the issue i guess. http://www.pcworld.com/article/157672/how_to_set_up_multiple_monitors.html