Registry problem? "... create an association in the Default Programs control panel"

Hi, sorry if this is in the wrong thread, and for the general newbieness of my situation. I removed the Win 7 Home Security 2011 rogue antispyware using this guide:
How to Remove Win 7 Home Security 2011 (Removal Instructions) | Faster, PC! Clean! Clean!
This involves manually editing the registry, which I had not done before. I believe I have removed the virus, but I encountered a slight problem; whenever I try to run most programs, such as games and D3Doverrider, I get this message: "This file does not have a program associated with it for performing this action. Please install a program or, if one is already installed, create an association in the Default Programs control panel." This error only appears if I choose to "Open" a file; everything works fine when I "Run as Administrator." This is more annoying than problematic, though I am worried that there might be problems that I am unaware of. I planned to give this tower to my mother soon, and I would very much like to fix this beforehand. I would be most grateful for any and all suggestions. Thank you.

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