If the InstallShield process froze, I doubt you'll make things any worse by killing the process, so try this:
Open up the Task Manager (Ctrl+Alt+Delete) and switch to the Processes tab and look for the InstallShield process. I don't know what it will be called. Hopefully it will say "InstallShield" somewhere in the description field, but if it doesn't, try looking for "iKernel.exe" or "setup.exe". End Process if you find it.