that first you have to reinstall the game using the default install directory C:\Program Files\TopGun – Hardlock for Win7 32 bit and C:\Program Files(x86)\TopGun – Hardlock for Win7 64 bit
Right klick on the topgun.exe, open properties compatibilty tab and enable the compatibility mode and change it to WINDOWS XP SP3, and tick RUN AS ADMINISTRATOR, klick OK and then go to c:\users\your Account name\my documents\my games and create a folder named:
TopGun – Hardlock.
It is possible that you dont need to change the compatibility mode i am not sure, but you must run the game as adminitrator.