I have this problem. I installed Windows 7 and the Windows 8 but if I try to log into Windows 7 after using Windows 8. All I get it a blank black screen that I have to power off the laptop by hard-pressing the power button. Is this a problem with the Bios?
You mentioned a USB hub in your title. Does Windows 7 boot normally if you don't have the USB hub connected?
Yes, it does. I have connected the usb hub with my Logitech nano receiver and Logitech usb headphone.