If you are having troubles logging into your Apple Developer account you will first need to ensure you are entering your login details correctly.
You will need to login through App Store Connect, NOT iTunes.
Here is the link to access App Store Connect if you should need it:
Please also ensure you are not logging in from a mobile device as Apple requires you to login from a Desktop or Laptop - they do not support mobile access.
If you continue to have issues logging in you will need to contact Apple directly.