when you have a dir, that is not chmod777, for the data on Windows, the page re-appears, but it doubles the ammount of s
so the first time its
and the second its \
eventually it says cannot find \\\\\\\\\\\\\\
that info is saved in the session, so when you re-try the install its says something like:
PHP ERROR: \\\\\\\\ cannot be found, and no form is shown, so you have to open another browser, and set the moodledata dir to 777.