OK, just figured out the same problem, hopefully that'll help somebody else so they don't have to re-install or do something else extreme.. So here's what you have to do: 1.
Get to the Advanced Boot Options menu by hitting F8 immediately after the BIOS screen and prior to Win boot - it's the screen where you can select 'Safe Mode', 'Last Good Configuration', etc.. 2.
Towards the bottom of the screen there is an option that says 'Disable Driver
Signature Enforcement' or something like that - choose that and [ENTER]. 3.
Watch your PC magically boot into Windows 7! 4.
Once you log in, open Command Prompt with administrative privileges and do a [sfc /scannow] - which will hopefully fix the broken driver.
Hope this works for you - it did for me! Good luck!