I'm not a Aperture expert but it seems to me that Aperture needs to process something. (thumbnails and previews usually)
Aperture from my brief experience with it, takes a long long time to process thumbnails and previews so would be best just to open Aperture when you don't need it or the computer, like overnight and let it just do its thing.
You can see what what Aperture is doing by pressing command+shift+0 (That's a zero)
Does it show anything when the activity window opens?