Welcome to the boat mate.
Did you remove all your mods, I see you have downloaded a lot.
Back them up if necessary and make sure non are left and delete the SH 4 folder if it's still there.
I would put the new install in it's own folder rather than Programs Files.
Program Files causes problems for some people.
Someone had this very problem a few months ago but I don't remember what he did, but it was something to do with mods I think.
Did you check out the install on vista thread?
Magic