You have not really got problems, you just do not see the post screen. Neither do I with my 670 and I am connected via DVI. But it might well be that my PC boots so quickly that it does not wait for scans of connections on my monitor to be completed before it boots to desktop.
In my case it also might be that my secondary monitor, a Dell Ultrasharp 24" shows as monitor one and my 27" shows as monitor 2. The 24" is connected via HDMI and of course the 27" is my main monitor.
Provided your PC is working fine then there is nothing to be concerned about.