Is your internet service just plain slow ?
I get the black screen as well... for about
two seconds!!
I think that if it was a system-wide problem , you wouldn't be the only one complaining about it. Everyone would be jumping up and down.
Something I did notice a while back (but it has since disappeared) was that when I logged in, it gave me the current time in Central Daylight Time for a split second and then the screen would "go black" and then correct itself to the Eastern Zone (where I live)