The issues you are experiencing suggest something is clearly not configured correctly, especially if you are able to access CSS pages just from repeatedly logging in and clicking Dashboard.
There is a Guide for setting up Xibo on IIS 8.5 on Windows Server 2012, I have included a link so that you can take a look and see if this helps with your own setup:
You may also find that other users beneath the Guide may be able to help you with your issue.