Alfresco share and repo are two separate web applications hence share login page may not have idea whether alfresco is running fine or not. It may possible Alfresco has not started successfully.
From log file can help you to determine whats going wrong, Search for exceptions in log file -- It will give you an idea what is going on.
You can also go to /alfresco instead of going to /share and log-in to admin console using admin credential (admin/admin). Once that works, check for /share and try to log-in.
Hope this will help.
