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 Win7 partition to install Win8 upon?

If so, boot into Win8 to run Repair which should add Win7 to the boot menu: System Recovery Options - Boot to in Windows 8

If not, install EasyBCD to Win8 to add Win7 to Dual Boot on the Add OS Entry tab. You should be able to figure out at Start>Computer which is the Win7 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.