[ubuntu] Installation problem via wubi.

Hi, i am a beginner, trying to install ubuntu via wubi. For some days i was trying ubuntu from a live cd. last night it went wrong- i was booting my pc through a live cd, and suddently power went off. Today when i tried to boot-install it did not run, and gave me error "authentication failed". I have win8 on c: drive. And d: is empty(i am trying to install ubuntu 11.10 on it).
Pls help