I started it up after unpacking, haven't done anything else. Also, I don't have the user data anymore as I had to reinstall my desktop since.as long as you still have it you can just copy over the user data from the old to the new game. and you should be able to continue your old save.
by default, the cheat menu should open when you press the pause key.
to get up your relationships with the girls you could try kplug. you would only have to install the kplug.dll and the IPA loader. you can then change relationship values in the personal diary. and once you are done just delete the kplug.dll again. a bit convoluted but it should work.
because I have no idea why the cheat menu doesn't work on a fresh download unless you did something to it.
I downloaded the JP installer for kplug and ticked all the options. Although if I saw it right, I shouldn't have picked the uncensor option.