this is how MS stops you from "downgrading" to windows 7, and why pc sales are plunging. they learned their lesson with Vista, and are hellbent to create an apple style "walled garden" inside the windows ecosystem (which is one of two reasons for win8 metro, the other being the tablet market... but in the end most people overlook the fact, that metro is designed to bring a walled garden to windows).
chances are you're missing firmware "downgrades"... and certain parts might only have windows 8 drivers... so you might have to replace them. what specifically is wrong is complicated by that root level infestation into your system by win8 (all the way into the bios)
assuming you removed win 8 "properly" and installed win 7, then the problem is most assuredly on the hardware side of things.
a friend of mine got a laptop with win8 on it and hated it. but after a quick web search i saw parts of it didn't have win7 drivers... so he was stuck. i had to install classic shell to fix most of the problem, and he's generally happy. but it just highlights the headache of removing win8