I have a Surface Pro 3 i5 and 8GB of ram and the same problem.
I've tried turning off fast start up with no change.
I have been on the phone with Microsoft multiple times, no change.
The Microsoft store even replaced my Surface and no change.
It is driving me nuts. I spent a lot of money, and expect the damn thing to start up the first time.
Another note, when it is stuck on the sign in screen with the rolling dots, the back of my Surface gets pretty warm like when it is in heavy use.
I've just given up and I'm now waiting for Windows 10. I have high hopes this will solve the problem. Knowing Microsoft though, who knows?