I had to help a friend out of this predicament a while ago.. what I ended up doing was taking my smartphone into the store (an Office Depot) and searching the models of the computers they had for sale to see what has Windows 7 drivers available. Found one (A Lenovo, couldn't tell you what kind), had to muck around because it would only boot from USB but not cdrom (???), but finally got into the 7 installer and cleared all eight partitions and installed windows 7.

Eight Goddamned partitions. What the hell.

What you describe is a feature of Windows 8, it's to ensure that a trusted source controls what runs on the hardware. Windows 8 is, as you've discovered, far more security conscious.