Hey if you are trying to Reinstalling your Windows 8 DP it asks you to enter a product key
I’m reinstalling Windows Developer Preview and need to enter a product key.
You need to Enter this KeyFor Windows 8 Developer Preview Product key: 6RH4V-HNTWC-JQKG8-RFR3R-36498For Server edition
of Windows 8 Developer Preview:Product key: 4Y8N3-H7MMW-C76VJ-YD3XV-MBDKV
Thanks to Microsoft employee Michael
for Providing Product key Source