after i upgrade the SLES 11 SP4 into SLES 12 SP3
what was your upgrade path? A direct jump? Was this a SLES11SP4 installation for the same architecture? Is this a physical or virtual server and what platform is it running on?
“black screen” is a bit ambiguous - is this just the X server displaying a black screen, while you are able to switch between consoles? Or do you have no console access at all, not even in text mode? Do you see some (X) cursor or, alternatively, text mode?
Are there any gettys running on the console ports? If you’re just missing X11 display manager login, do you actually have an X server running? Does it get started at all and if not, what’s your default systemd target (AKA “run level”)? I If the X server gets started but dies, what’s in its logs?
IOW: More details, please - only that way we’ll be able to truly help.