Windows 7: What happens if I install Windows 8 on a separate partition?

OK, I think I just made a huge mistake here -- I installed Windows 8 Consumer Preview, and now Windows 7 doesn't boot up. What could this mean? Did I do something wrong? ...Any help?

Did you follow the steps in Dual Boot Installation - Windows 8 and Windows 7 or Vista? If so it should present a Dual Boot menu when it starts to choose which OS to boot.

Did you make sure that you weren't selecting the Windows 7 partition to install Win8 upon?

If so, boot into Win8 to run Repair which should add Windows 7 to the boot menu: System Recovery Options - Boot to in Windows 8

If not, install EasyBCD to Win8 to add Windows 7 to Dual Boot on the Add OS Entry tab. You should be able to figure out at Start>Computer which is the Windows 7 partition so you have its letter if required.

Good news, and bad news... I was able to get Windows 7 back, but my only problem is that in Windows 8, the start screen looks warped and the desktop is just a blank screen.

Did you run Automatic Repair from Win8 System Recovery Options - Boot to in Windows 8.
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Run it several times if necessary.