I didn't purchase an AGEOD title from Matrix yet, but both companies use a different installer. For Matrix games you always have to enter the serial at the start of installation process. If you encounter trouble here, do as I said: install on drive d:\, utilize admin mode for setup.exe (this is the installation file which ends with the suffix .exe) and sometimes you also have to run the game with the according file from it's subdirectory in admin mode.
However, AGEOD games are mostly available as demos and can be subsequently upgraded by serial. As far as I remember, WW1 Gold even offered a full-fledged 14 days free trial before one had to register it. Anyway, if you absolutely can't make it work, or suspect your serial is invalid, but desperately want to play it now: uninstall the game, delete registry-entries and do a fresh install of the demo. This should give you some free playtime. Meanwhile send an e-mail (not pm) to Erik Rutins. He is usually fast with solving issues.