ok so i just got my step dads computer back
Back from what? repair? upgrade?...............that might have something to do with it.

Install shield is common software that ships with apps. It installs the app, the uninstall information and clears out temporary files. It should close/delete itself when it has finished

Rider_Royal has a good suggestion..............you may have had something that failed to install earlier.

What is your operating system if it is XP or Win2000 you need to be logged in with an account that has the authority to load software.

Cheers

EDIT: OK I have just checked this machine, and I don't have installshield.exe anywhere on it. I didn't expect to find it as it should delete itself when finished. To be safe rename yours to installshield.txt and try installing your game again.