I am trying to understand how an Acer Vista Premium License key will work with correct Acer recovery media but not with OEM Vista Premium DVD. This has nothing to do with the motherboard. It has everything to do with the OS. I bought the Acer AM5640 without windows or recovery disk. It had Acer Vista Home Premium License Key on the Side. I used my OEM Vista Home Premium DVD to load windows but it said license key was invalid. I sold the motherboard from the machine and replaced it with an ECS motherboard with same chipset. After trying several things I mentioned in another post, I ordered the recovery media from Acer and loaded it on the Acer Computer (with ECS Motherboard purchased off Ebay installed- NOT AN ACER Board -). After installing recovery media, I used the Acer OemAct Vista Home premium number on the side of the case and it worked and activated. This tells me (1) in this case the motherboard has nothing to do with this License Key. (2) The key is specific to the Acer Recovery Media Question? Is there some file in the Vista Installation that says accept only Keys starting with K or P for this computer? I would love to figure out how the Vista knew not to allow this valid key to work with an oem Home Premium version of Vista. When I called Microsoft, they also gave me another key for this computer that came back invalid with my oem install but I bet it would work with this acer recovery installation. I would love to figure out what mods I would have to make to get this to work with OEM Vista Home Premium. Any ideas?