Looking at your post all I see is the usual story but have to guess someone installed Windows and didn't finish the install.
I can't offer the exact procedure but the maker of the machine should be keel hauled until they tell you the exact and working install plan.
i recently purchased and built my 4th custom pc. i build them once every 4 years or so to keep up to date with the latest games and hardware. my new rig features an AMD FX-6200 6-core processor, and a sapphire radeon HD 6950 2gb video card. as well as 8gb ddr3 ram. now for some reason, this machine will get jittery frames and/or even worse frames than my previus machine (featuring an AMD Athlon II x2 220, with a radeon HD6670 1gb) this only happens in some games though. like Portal 2, Minecraft, and Diablo 3. while in every other game, this rig performs outstandingly better than the old one. if anyone knows the answer i would be very grateful for your advice