Can't Install Exe File: Registy Mechanice

for 2 days iv been really pulling my hair out with why i cant install a exe file.. I remember installing Registy Mechanic before hand and if i remember rightly a year or so ago i did the same thing but for the life of me i cannot remember why or what i did to sort it out! I have looked everywhere to work out what is wrong with my system and i really cant work out whats happend..This particular .exe file is for the sims 3 and when i try to click the .exe file it gives me this box with this information in it..

Code:
Windows ® Installer. V 4.5.6002.18005
msiexec /Option <Required Parameter> [Optional Parameter]
Install Options
</package | /i> <Product.msi>
Installs or configures a product
/a <Product.msi>
Administrative install - Installs a product on the network
/j<u|m> <Product.msi> [/t <Transform List>] [/g <Language ID>]
Advertises a product - m to all users, u to current user
</uninstall | /x> <Product.msi | ProductCode>.........................