help me play sim city 4 again

I have owned and played sim city 4 for years with no problems on my computer, the same computer I have played it on before. I had the urge to play the other day and I get a message that pops up saying access denied please login with administrator privileges and try again. I am under the administrator account and I have read tips about granting access to everyone under properties of the game and nothing has worked. I tried uninstalling and reinstalling the game and that did not work as well. All I wanted to do was play my game and instead I monkeyed with my computer for about an hour trying to get the game running. Anyone that can help I would appreciate it I would hate to have to buy this game again in a download version. I have heard some people say they can redeem the code in the box for a free download any clues guesses or anything would help.