Hi,
This is interesting. I have an SP3 which at start-up hangs at the Surface logo, i.e. Windows won't start. I have been looking into this since the beginning of March 2016. Sure, the 2-button restart works. I have really mastered the technique now and can
do it in less than 5 minutes :-) The latest suggestion from the very helpful Barb Bowman is to re-image. That's a lot of work for me and, in my humble opinion, does not have a high probability of success.
The connection between this thread and my SP3 hanging is that I stumbled across "Intermittent problems occur while peripherals are attached to a Surface Pro 3 device". Pursuing this leads to a hotfix dated August 2015. As of May 2016 this hotfix remains
untested and there are plenty of warnings that I'll be on my own if I apply it and there's no cure or worse.
Now, here's the rub. The hotfix asks me to check in Device Manager / Surface Pro System Aggregator Firmwarethat the version after installation is 3.9.450.0 [dated 29 July 2015]. When I checked that a few days ago I found I'm on version 3.9.750.0 dated 28 September
2015. I conclude that it doesn't seem wise to apply this "fix"; for details see https://support.microsoft.com/en-us/kb/3087655
I guess the screen, as seen by an SP3 or SP4, is just another device which the Surface Pro System Aggregator Firmware sometimes fails to successfully enumerate.
What version of this firmware are you guys with SP4's on?
I'm now hoping that the next major release of Windows 10, "Redmond" slated for June / July, will address the problem but I don't think this type of problem is high on the list of Microsoft's priorities.
My SP3 is still under guarantee. It'll be a shame if I have to return it and try to get my money back on the basis that being able to use it as a laptop replacement is "not as described" and "not fit for purpose" (UK English legal jargon).