Why won't my sims 2 downloads install?

I've been using the sims 2 for a long time, but recently changed to a brand new computer and I'm experiencing problems downloading things from the sims 2 site.
When I download something from the exchange, I save the file then double click to open it. Rather than the usual message asking if I would like to install the simpack, a message appears from User Account Control asking me "Do you want the following program from an unknown source to make changes to this computer?" As usual, I click "yes" and the window leaves. However, nothing more comes up, and nothing installs to my game.
I've never had this happen before and do not know why it is happening.
Any help or advice on how to solve the issue would be greatly appreciated.

Note: The game is newly installed with no mods to speak of, and reintallation has been no help. My computer is a PC; an HP Pavilion P6000 Series, Model No.
p6517c, if that helps.
 
I not played sims 2 in years but I always manually added the content to the folders, all simpack does it put the correct files in the right place I believe, can you not manually open with simpack, right click open with, Sims 2 and it be in there somewhere. I think sims 2 even added a folder for you to drop stuff into in my documents, but like I said Ive not played it in years,
 
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