Does anyone know of a safe site from where I can download this game? Big Fish is not an option, as I can't access any games I have purchased from them before a certain date.

Thanks in advance,

Doreen

There are no legal download sites for Riddle of the Sphinx.
You can buy a disc version from the allvideo guy on eBay or on his website. That's not a downloaded version though, it's the original game on CD plus an installer disc that runs the game in tweaked DOSBox on modern Windows.

I think Big Fish should help you with your problem accessing your games though -- unless it's a problem with the game not being compatible with your Windows version and not to do with the Games Manager.