It is not possible to recover Windows from there. You'll need the Windows DVD (Windows 7 DVD for example if you have Windows 7). Boot the DVD up, select Recovery. When it offers to repair it automatically, say no.
recovery prompt and type these commands one-by-one:
After you have done this, close the prompt with the X, and close the Windows 7 installer. Reboot, there you go.
(As a side note: Wubi is not really recommended. It's really just for playing around. As you experienced, the system may break very easily even with some updates. You should just resize your main partition with the Windows partition manager or some commerical software like
Acronis Disk Director and install Ubuntu to a new partition.)