Use a tool like phpMyAdmin to check your databases directly.
Open the (your db prefix)_options
table in the database for the problem site.
Then check the row where option_name = siteurl
and see if the option_value
is correct.
If not, correct it and you will be able to login to the wp-admin of that site.
You may still need to correct other urls too; this is a good tool for changing urls.