Mbp retina medio 2012, black screen with 'start-up sound'

Hello!

I'm a bit freaking out right now, i have a mbp pro 2012 retina with osx mavericks on it.

today was the day i wanted to update the os to the latest from apple. But yesterday evening when i woke up my mbp from its sleepmode, it started up, and then the screen went black.

i Couldn't get it back, and even though i closed the mbp, i could still hear it running.

so today i tried to connect it to an external screen (only worked when the screen on the mbp worked).

i Tried different reset options including the reset of the controller with the control option shift I/O button.

i Tried to start it up in safe mode, after hearing the tune, pressing shift

i tried the option command p+ r after starting op the mac.

the latest option succeeded once, then i directly tried to make a backup with my time machine hard drive, but them again in the middle of the backup te screen went dark.

i Have no clue what to do right now... Is there anybody able to help me or might have any experience with this?

(i personally suspect a software problem)

thanks!