SharePoint 2013 Blank login page and other login issues

Theres a few reasons for a blank SharePoint page after login*. It usually means you have an issue with the AD account.

The most common reasons are:

1. Username/Password incorrect
1. With 3 failed attempts usually
2. The AD User has "change password after login" enabled

* Strangely there's no failed login page, just a blank page

If you are getting a request access screen when you already have access:

1. Check the Security access page that the group the user is in has access
2. Try removing the user from the group and re-adding them
3. If there was a migration from 2010 to 2013 the accounts have to be upgraded to use claims