You should not install Windows 8 Developer Preview on your main computer - it's not even a beta product yet and bugs are to be expected.
From the main download page:
The Windows Developer Preview is a pre-beta version of Windows 8 for developers. These downloads include prerelease software that may change without notice. The software is provided as is, and you bear the risk of using it. It may not be stable, operate correctly
or work the way the final version of the software will. It should not be used in a production environment.
Also, it is stated on the Windows Developer Preview download page that you must reinstall the previous OS:
Notes about installing the Windows Developer Preview
You can't uninstall the Windows Developer Preview. To reinstall your previous operating system, you must have restore or installation media.