You can try uninstalling the entire game, then check for any left over folders, delete them if found.
Then check for any of the following Keys, delete them if found;
Then launch the System Registry (Start-> run, and type regedit)
Look for and delete the following Keys;
HKEY_LOCAL_MACHINE\SOFTWARE\Stardock\Drengin.net\sins
HKEY_LOCAL_MACHINE\SOFTWARE\Stardock\Drengin.net\sinsentrench
For Vista 64 bit;
HKLM>SOFTWARE>Wow6432Node>Stardock>Drengin.net>sins
HKLM>SOFTWARE>Wow6432Node>Stardock>Drengin.net>sinsentrench
Reboot your PC, and re-install