FIXED! For me anyway.....

If anyone is still interested, I had a nightmare resolving this issue only yesterday.. Tried everything I could think of, no small amount of head scratching and then finally I stumbled upon the solution.

I noticed that the Folder/File permissions were absolutely trashed when installing SQL Server to the root of a drive. I simply created a folder on the root of the particular drive and set that folder as the install directory for SQL... Reeling back in shock as I realised that this worked. SQL Agent started automatically after install using the credentials NT Service\SQLAgent$InstanceName to start the service. 🙂 HAPPY DAYS!

Hope that helps someone !

Paul